Working in progress: https://chromium-review.googlesource.com/c/chromium/src/+/1380947

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9

commit d90b8d0e009ab80f52fd50127cc90ca45bbc99c9
Author: Liquan(Max) Gu <maxlg@chromium.org>
Date: Fri Jan 04 15:53:33 2019

[FCP++] Stop recording new entries upon user input

Currently, FCP++ records new image and text for the whole life cycle of a tab.
However, FCP++ should only be interested in the elements attached before user
input. This is because user input can cause changes to the DOM. That's why
FCP++ need to stop recording new elements upon user input.

The CL causes behavior changes to FCP++.
* When users give input other than kMouseMove, kMouseEnter, kMouseLeave and
pinches, FCP++ deactivate its detectors. Note that the user inputs include
both those handled by mainthread (click, touch, etc) and compositor thread
(off-mainthread scrolling, gesture, etc). But these exclude the input events
that have been filtered from the browser side.
* When deactivated, the text and image detector stops to record new entries
and node removal. But they still observe the loading status. In other words,
if an image is recorded before deactivation, and finish loading after
deactivation, the image paint detector can still observe the loading being
finished.

Bug:  915804 
Change-Id: I49d3d9aa0b2e73a4775147ff1a2bb4b065c5b9b2
Reviewed-on: https://chromium-review.googlesource.com/c/1380947
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Liquan (Max) Gu <maxlg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619960}
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/exported/web_view_impl.cc
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/image_paint_timing_detector.cc
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/image_paint_timing_detector.h
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/image_paint_timing_detector_test.cc
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/paint_timing_detector.cc
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/paint_timing_detector.h
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/text_paint_timing_detector.cc
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/paint/text_paint_timing_detector.h
[modify] https://crrev.com/d90b8d0e009ab80f52fd50127cc90ca45bbc99c9/third_party/blink/renderer/core/scroll/scrollable_area.cc