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

third_party/WebKit/Source/core/dom/TouchInit.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://w3c.github.io/touch-events/#touch-interface
 
 dictionary TouchInit {
     required long        identifier;
     required EventTarget target;
              double      clientX = 0;
              double      clientY = 0;
              double      screenX = 0;
              double      screenY = 0;
              double      pageX = 0;
              double      pageY = 0;
              float       radiusX = 0;
              float       radiusY = 0;
              float       rotationAngle = 0;
              float       force = 0;
+
+             // Canvas HitRegion
+             // https://github.com/whatwg/html/issues/547
+             // TODO(zino): This attribute should be declared as partial dictionary but

[Rick Byers, 2016/03/10 21:36:29]

nit: remove the TODO now that we're not using partial dictionaries at all here.

[zino, 2016/03/11 09:35:47]

Done.

+             // IDL parser can't support it yet. Please see: http://crbug.com/579896
+             DOMString? region = null;
 };