The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/89a0720b870e152afbbe64f6dd9d15556645e2b0

commit 89a0720b870e152afbbe64f6dd9d15556645e2b0
Author: Joel Einbinder <einbinder@chromium.org>
Date: Tue Mar 27 03:21:13 2018

DevTools: Update page scale immediately in InputHandler

Input handler was recieving the page scale after a frame was rendered,
which caused a race when sending mouse events after the page scale was
change but before the next frame was rendered.

This patch listens directly to the page scale changes.

Bug:  826012 

Change-Id: I40ea7342f075aacde762a65dda7f71257f584a11
Reviewed-on: https://chromium-review.googlesource.com/969717
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545955}
[modify] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/content/browser/devtools/protocol/input_handler.cc
[modify] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/content/browser/devtools/protocol/input_handler.h
[modify] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/content/browser/devtools/render_frame_devtools_agent_host.cc
[modify] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/content/browser/devtools/render_frame_devtools_agent_host.h
[add] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/third_party/WebKit/LayoutTests/inspector-protocol/input/dispatchMouseEvent-emulated-viewport-expected.txt
[add] https://crrev.com/89a0720b870e152afbbe64f6dd9d15556645e2b0/third_party/WebKit/LayoutTests/inspector-protocol/input/dispatchMouseEvent-emulated-viewport.js