The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c6e050f06efedae49f77dd91baa016dbd2e8fe9

commit 2c6e050f06efedae49f77dd91baa016dbd2e8fe9
Author: nzolghadr <nzolghadr@chromium.org>
Date: Wed Sep 07 17:40:49 2016

The first step of separating mouse code from EventHandler.

There will be follow up CLs to refactor more code and
address the TODOs added in this CL.

Creating MouseEventManager to encapsule mouse related
bookkeeping and dispatching.

Creating abstract BoundaryEventDispatcher to keep the
boundary node elements calculation so PEM and MEM can
make subclasses from it and send their own boundary events.

Creating EventHandlingUtil to share the common functions
used in different EventHandling path instead of putting
them all as static in EventHandler.

BUG= 625843 

Review-Url: https://codereview.chromium.org/2255323004
Cr-Commit-Position: refs/heads/master@{#416984}

[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/events/MouseEvent.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/html/HTMLLabelElement.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/BUILD.gn
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/BoundaryEventDispatcher.cpp
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/BoundaryEventDispatcher.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/EventHandler.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/EventHandler.h
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/EventHandlingUtil.cpp
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/EventHandlingUtil.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/GestureManager.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/GestureManager.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/KeyboardEventManager.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/KeyboardEventManager.h
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/MouseEventManager.cpp
[add] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/MouseEventManager.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/PointerEventManager.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/PointerEventManager.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/ScrollManager.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/ScrollManager.h
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/TouchEventManager.cpp
[modify] https://crrev.com/2c6e050f06efedae49f77dd91baa016dbd2e8fe9/third_party/WebKit/Source/core/input/TouchEventManager.h