Canvas2d: Implement rerouting event by hit region's control.

third_party/WebKit/Source/core/events/MouseEventInit.idl

Index: third_party/WebKit/Source/core/events/MouseEventInit.idl
diff --git a/third_party/WebKit/Source/core/events/MouseEventInit.idl b/third_party/WebKit/Source/core/events/MouseEventInit.idl
index cbb4d7d83781cf975b530f6450f09681fc714900..20c94eae85452b5f1d2bdabe78a2de4ed4668554 100644
--- a/third_party/WebKit/Source/core/events/MouseEventInit.idl
+++ b/third_party/WebKit/Source/core/events/MouseEventInit.idl
@@ -17,4 +17,10 @@ dictionary MouseEventInit : EventModifierInit {
     // https://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html#extensions-to-the-mouseeventinit-dictionary
     long movementX = 0;
     long movementY = 0;
+
+    // Canvas HitRegion
+    // https://html.spec.whatwg.org/multipage/scripting.html#MouseEvent-partial
+    // TODO(zino): This attribute should be declared as partial dictionary but
+    // IDL parser can't support it yet. Please see: http://crbug.com/579896

[Rick Byers, 2016/02/23 20:26:08]

Since I don't think this is going to happen anytime soon, how about we just make
everything nice and consistent and move the trivial
MouseHitRegion/TouchHitRegion code directly into MouseEvent and TouchEvent?  Now
that it's a simple accessor the implementation is really trivial, probably more
confusion than benefit to trying to have it separated out into modules/canvas2d

[zino, 2016/03/08 12:33:48]

Done.

+    DOMString? region = null;
 };