The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4

commit 3d5ac6c509cfc5eadfde5748447791d25ee9e7a4
Author: Lan Wei <lanwei@chromium.org>
Date: Thu Dec 13 21:21:14 2018

Make pressing multi-button pass on wpt serve

In order to support pressing multi-button at the same time, we keep the
buttons that were pressed before in the modifiers when passing to
InputHandler::DispatchMouseEvent function. Also, we support back and
forward buttons.

This patch makes
wpt/pointerevents/pointerevent_pointermove_on_chorded_mouse_button.html
wpt/uievents/mouse/mouse_buttons_back_forward.html pass.

Bug:  913633 
Change-Id: I525812abfa523644a573b25499bf7246a787f538
Reviewed-on: https://chromium-review.googlesource.com/c/1371031
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616437}
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/chrome/test/chromedriver/chrome/ui_events.cc
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/chrome/test/chromedriver/chrome/ui_events.h
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/chrome/test/chromedriver/chrome/web_view_impl.cc
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/chrome/test/chromedriver/element_commands.cc
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/chrome/test/chromedriver/window_commands.cc
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/content/browser/devtools/protocol/input_handler.cc
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/content/browser/devtools/protocol/input_handler.h
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/renderer/core/inspector/browser_protocol.pdl
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/inspector-protocol/dom/dom-setInspectModeEnabled.js
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/inspector-protocol/input/dispatchMouseEvent-ack.js
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/inspector-protocol/input/dispatchMouseEvent-expected.txt
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/inspector-protocol/input/dispatchMouseEvent.js
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/inspector-protocol/sessions/input-dispatch-mouse-event.js
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/platform/linux/inspector-protocol/input/dispatchMouseEvent-expected.txt
[modify] https://crrev.com/3d5ac6c509cfc5eadfde5748447791d25ee9e7a4/third_party/blink/web_tests/platform/win/inspector-protocol/input/dispatchMouseEvent-expected.txt