Internal thread discussing this here: https://groups.google.com/a/google.com/d/msg/chrome-input/_tyas1nNmfk/lxevE5O3CAAJ

There's some risk of breakage here, so I think we intend to follow the intervention process (guide, measure, etc.).  But I'm optimistic there are some good wins available.

Note that this should include skipping the touch-action computation (Edge doesn't do it either during a fling - see issue 631899).  Perhaps we can safely ignore the explicit passive:false regions too.

In addition to better repeated fling performance, this should also generally be  a better UX.  When you're repeatedly flinging a scroller, you don't expect it to suddently stop moving if you happen to do one of the flings overtop of an element that cancels the touch or disables the scroll via touch-action.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159

commit 59bb2579a58499fc1f8f9e2ccc0ef5c930d34159
Author: lanwei <lanwei@chromium.org>
Date: Mon Aug 15 23:29:52 2016

Add flag to force touch events to be passive during fling as a runtime feature.

We are forcing touchstart and first touchmove to be passive during fling as our part of
intervention. Now we add a flag to turn on this feature at runtime.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2244503003
Cr-Commit-Position: refs/heads/master@{#412094}

[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/chrome/app/generated_resources.grd
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/chrome/browser/about_flags.cc
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/content/child/runtime_features.cc
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/content/public/common/content_features.cc
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/content/public/common/content_features.h
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/third_party/WebKit/public/web/WebRuntimeFeatures.h
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/tools/metrics/actions/actions.xml
[modify] https://crrev.com/59bb2579a58499fc1f8f9e2ccc0ef5c930d34159/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0

commit 4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0
Author: lanwei <lanwei@chromium.org>
Date: Fri Aug 19 18:23:11 2016

Make first TouchStart and first TouchMove events on a flinging layer non-blocking.

Blocking touchstart and first touchMove handlers during fling can cause major hiccups during
fling boosting / flywheel fling.

We are doing a passive event listener during fling intervention experiment to see if we can
improve the fling performance by forcing touchstart and first touchmove to be passive when
there is an active fling animation.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2233543002
Cr-Commit-Position: refs/heads/master@{#413189}

[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/browser/renderer_host/input/touch_event_queue.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/browser/renderer_host/input/touch_event_queue_unittest.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/common/input/event_with_latency_info.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/common/input/event_with_latency_info_unittest.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/renderer/input/main_thread_event_queue.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/renderer/input/main_thread_event_queue.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/renderer/input/main_thread_event_queue_unittest.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/renderer/input/render_widget_input_handler.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/content/renderer/render_widget_unittest.cc
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/core/events/Event.cpp
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/core/events/Event.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/core/input/TouchEventManager.cpp
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/core/input/TouchEventManager.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/platform/PlatformEvent.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/platform/PlatformTouchEvent.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/Source/web/WebInputEventConversion.cpp
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/third_party/WebKit/public/platform/WebInputEvent.h
[modify] https://crrev.com/4cc123442a0ef00e377d7e9b8703ba3bf4c6b5a0/tools/metrics/histograms/histograms.xml

[Automated comment] Commit may have occurred before M54 branch point (8/25/2016), needs manual review.

M54 is not branched yet so removing "Merge-Review-54" label.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/90281ac261437a8bf316f799749ef4403c26de0b

commit 90281ac261437a8bf316f799749ef4403c26de0b
Author: lanwei <lanwei@chromium.org>
Date: Thu Sep 01 22:39:01 2016

Enable PassiveEventListenersDueToFling on waterfall.

Enable passive touch event listeners due to fling finch experiment on waterfall.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2306723002
Cr-Commit-Position: refs/heads/master@{#416092}

[modify] https://crrev.com/90281ac261437a8bf316f799749ef4403c26de0b/testing/variations/fieldtrial_testing_config_android.json
[modify] https://crrev.com/90281ac261437a8bf316f799749ef4403c26de0b/testing/variations/fieldtrial_testing_config_chromeos.json
[modify] https://crrev.com/90281ac261437a8bf316f799749ef4403c26de0b/testing/variations/fieldtrial_testing_config_linux.json
[modify] https://crrev.com/90281ac261437a8bf316f799749ef4403c26de0b/testing/variations/fieldtrial_testing_config_mac.json
[modify] https://crrev.com/90281ac261437a8bf316f799749ef4403c26de0b/testing/variations/fieldtrial_testing_config_win.json

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99

commit 8f1957b19f5c0e8e09dc98480c613e2e5c59cd99
Author: lanwei <lanwei@chromium.org>
Date: Tue Nov 08 17:09:25 2016

In the previous patch, https://codereview.chromium.org/1923973002/, we added a is_fling flag
to indicate if the active fling is happening on either main or impl thread.

Now we only consider about scrolling happening in impl thread and we will use ack states to
indicate if we want to make the touch events uncancelable.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2479023003
Cr-Commit-Position: refs/heads/master@{#430640}

[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/blimp/client/core/input/blimp_input_handler_wrapper.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/blimp/client/core/input/blimp_input_handler_wrapper.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/browser/renderer_host/input/input_router_impl.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/common/input/input_event_ack_state.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_event_filter.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_event_filter.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_handler_manager.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_handler_manager.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_handler_manager_client.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_handler_wrapper.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/input_handler_wrapper.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/main_thread_event_queue.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/main_thread_event_queue.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/input/main_thread_event_queue_unittest.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/mus/compositor_mus_connection_unittest.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/content/renderer/render_widget_unittest.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/third_party/WebKit/Source/platform/PlatformTouchEvent.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/third_party/WebKit/Source/web/WebInputEventConversion.cpp
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/third_party/WebKit/public/platform/WebInputEvent.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/ui/events/blink/input_handler_proxy.cc
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/ui/events/blink/input_handler_proxy.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/ui/events/blink/input_handler_proxy_client.h
[modify] https://crrev.com/8f1957b19f5c0e8e09dc98480c613e2e5c59cd99/ui/events/blink/input_handler_proxy_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/53c12368f78425a27d592f47f814029cf2edaae7

commit 53c12368f78425a27d592f47f814029cf2edaae7
Author: lanwei <lanwei@chromium.org>
Date: Tue Nov 29 06:51:17 2016

Make touch events uncancelable during fling when they are on the current active scroll layer

In the previous patch https://codereview.chromium.org/2233543002/, we missed to check if the
touch events which we will make uncancelable when there is an active fling are on the
same layer as the current active scroll layer or its descendants.

Now, we add the scroll layer check here to minimize the breaking cases and also match with other
browsers' behavior, such as Safaris and Firefox.

This code has two parts:
1. Delete the is_fling flag we used on https://codereview.chromium.org/1923973002/
to indicate if the actice fling is happening.
2. Add check to the touch start if it hits on the same layer as the current active scroll layer.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2471523002
Cr-Commit-Position: refs/heads/master@{#434917}

[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/cc/input/input_handler.h
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/cc/trees/layer_tree_host_impl.cc
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/cc/trees/layer_tree_host_impl.h
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/cc/trees/layer_tree_host_impl_unittest.cc
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/content/renderer/input/input_handler_manager.cc
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/ui/events/blink/input_handler_proxy.cc
[modify] https://crrev.com/53c12368f78425a27d592f47f814029cf2edaae7/ui/events/blink/input_handler_proxy_unittest.cc

Let's leave this Started until we've shipped it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/79570682b716962ae9cfd22df7277112b8df8d74

commit 79570682b716962ae9cfd22df7277112b8df8d74
Author: lanwei <lanwei@chromium.org>
Date: Fri Dec 09 12:18:34 2016

Remove PassiveEventListenersDueToFling from WebRuntimeFeatures

This intervention only changes code in CC, so We do not need this flag in Webkit,
removing the flag from Webkit's WebRuntimeFeatures.

BUG= 595327 

Review-Url: https://codereview.chromium.org/2559283002
Cr-Commit-Position: refs/heads/master@{#437520}

[modify] https://crrev.com/79570682b716962ae9cfd22df7277112b8df8d74/content/child/runtime_features.cc
[modify] https://crrev.com/79570682b716962ae9cfd22df7277112b8df8d74/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
[modify] https://crrev.com/79570682b716962ae9cfd22df7277112b8df8d74/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
[modify] https://crrev.com/79570682b716962ae9cfd22df7277112b8df8d74/third_party/WebKit/public/web/WebRuntimeFeatures.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/176226667ce5adc58e636ebf31049acff46810b2

commit 176226667ce5adc58e636ebf31049acff46810b2
Author: lanwei <lanwei@chromium.org>
Date: Fri Dec 09 15:26:28 2016

Enable PassiveDocumentEventListeners feature

We decide to ship the intervention of 'Uncancelable Touch Events During A Fling',
so enable 'PassiveDocumentEventListeners' feature.

Below is the link to the discussion on blink-dev
https://groups.google.com/a/chromium.org/d/topic/blink-dev/wJGmsdYxwrg/discussion

BUG= 595327 

Review-Url: https://codereview.chromium.org/2556723006
Cr-Commit-Position: refs/heads/master@{#437544}

[modify] https://crrev.com/176226667ce5adc58e636ebf31049acff46810b2/content/public/common/content_features.cc

Issue 646069 has been merged into this issue.

Moving to Launch-OWP to make this web platform change public.
This shipped in M57, right?  Marking 'Fixed' to properly track it's status.

Also updated chromestatus entry to point here and properly mark this as shipping in M57: https://www.chromestatus.com/feature/5707400183021568

Spec issue: https://github.com/w3c/touch-events/issues/76