It seems like this would involve changing window-focus behavior such that we send the background window the mouse-down event but don't focus it until mouse-up.

@oshima what do you think?

It's a bit tricky because we still should active a window on mouse click in normal case.

One approach is to add a private API to not to activate by default, but let an app decide when to activate (or not). 

I'll aura/ash API, then yamaguchi@ can use it from files app to implement this behavior.

> I'll aura/ash API,

oops, it should read: I'll add aura/ash API, then...

warx@, can you work on this? I can explain offline

I had a chat with yamaguchi@ about the proposal of setActivateOnClick(bool) API.

Attach his comments here for a record, "setActivateOnClick(bool) sounds enough. Assuming that there's already another API that the app can activate itself whenever it wants. What we'd do on our side (file_manager) is: 1. ask the window manager not to activate the window on click, but want all mouse events 2. ask window manager to activate the window whenever the app wants (for example, on mouseup event handler)."

If we also want the same for dragging a file by touch, we'll also need to prevent activating a window at touch start.

Consider naming it SetActivateOnPointer so that it's clear the function applies to activation by any pointer, not just mouse.

For dragging by touch induced window activation, it will be handled by OnGuestureEvent here: [1]. I believe that is why OnTouchEvent is not implemented in FocusController?

FocusController only deals with focusing window for two input events, OnMouseEvent with mouse_pressed and OnGestureEvent with gesture_begin and touch_points() == 1. I agree changing the name to SetActivationOnPointer to cover both cases.

[1] https://cs.chromium.org/chromium/src/ui/wm/core/focus_controller.cc?q=focus_controll&l=139

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e47fb498dce50d65d9c3b55fafdbffbe50ab6920

commit e47fb498dce50d65d9c3b55fafdbffbe50ab6920
Author: warx <warx@chromium.org>
Date: Fri Apr 28 02:20:14 2017

cros: allow aura window not considered activatable for pointer event

Changes:
Add a window property for set/get whether an aura window is considered activatable for pointer window activation. Modify CanFocusWindow in FocusRules to allow optional check for ui::Event.
This is a stage one implementation for crbug.com/657525.

BUG=657525
TEST=added test coverage

Review-Url: https://codereview.chromium.org/2809073002
Cr-Commit-Position: refs/heads/master@{#467849}

[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ash/wm/ash_focus_rules.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ash/wm/ash_focus_rules.h
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ash/wm/window_manager_unittest.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/aura/client/aura_constants.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/aura/client/aura_constants.h
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/base_focus_rules.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/base_focus_rules.h
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/focus_controller.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/focus_controller.h
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/focus_controller_unittest.cc
[modify] https://crrev.com/e47fb498dce50d65d9c3b55fafdbffbe50ab6920/ui/wm/core/focus_rules.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dc2e682ca5558e90332f8443e23539a04f436273

commit dc2e682ca5558e90332f8443e23539a04f436273
Author: warx <warx@chromium.org>
Date: Tue May 09 18:39:31 2017

cros: Hook AppCurrentWindowInternal setActivateOnPointer with aura side api

Changes:
This is a follow up CL of https://codereview.chromium.org/2809073002/, which hooks AppCurrentWindowInternal setActivateOnPointer API with aura side changes.

BUG=657525
TEST=none

Review-Url: https://codereview.chromium.org/2854893004
Cr-Commit-Position: refs/heads/master@{#470390}

[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.mm
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/chrome/browser/ui/views/apps/chrome_native_app_window_views_aura_ash.cc
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/chrome/browser/ui/views/apps/chrome_native_app_window_views_aura_ash.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/browser/api/app_current_window_internal/app_current_window_internal_api.cc
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/browser/api/app_current_window_internal/app_current_window_internal_api.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/browser/app_window/native_app_window.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/browser/extension_function_histogram_value.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/common/api/app_current_window_internal.idl
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/components/native_app_window/native_app_window_views.cc
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/components/native_app_window/native_app_window_views.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/shell/browser/shell_native_app_window.cc
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/extensions/shell/browser/shell_native_app_window.h
[modify] https://crrev.com/dc2e682ca5558e90332f8443e23539a04f436273/tools/metrics/histograms/enums.xml

Pass the issue to yamaguchi@

Unassigned for triage in the Files app team.
The remaining tasks for this feature is inside the Files app.

weifangsun@ could you please triage?

Checked with afakhry@ on prioritization, updated component, added to Files app backlog for future work.