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

third_party/WebKit/Source/platform/PlatformMouseEvent.h

Index: third_party/WebKit/Source/platform/PlatformMouseEvent.h
diff --git a/third_party/WebKit/Source/platform/PlatformMouseEvent.h b/third_party/WebKit/Source/platform/PlatformMouseEvent.h
index 7051f901b33a88afeb4041f4e344d03ffc02a4ea..f43a2448ae8bf9d0cb92ad9ae542def630a845a4 100644
--- a/third_party/WebKit/Source/platform/PlatformMouseEvent.h
+++ b/third_party/WebKit/Source/platform/PlatformMouseEvent.h
@@ -29,6 +29,7 @@
 #include "platform/PlatformEvent.h"
 #include "platform/geometry/IntPoint.h"
 #include "public/platform/WebPointerProperties.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
@@ -87,6 +88,9 @@ public:
     bool fromTouch() const { return m_synthesized == FromTouch; }
     SyntheticEventType syntheticEventType() const { return m_synthesized; }
 
+    const String& region() const { return m_region; }
+    void setRegion(const String& region) { m_region = region; }
+
 protected:
     WebPointerProperties m_pointerProperties;
 
@@ -101,6 +105,9 @@ protected:
     MouseButton m_button;
     int m_clickCount;
     SyntheticEventType m_synthesized;
+
+    // For canvas hit region.
+    String m_region;

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

Conceptually this would probably make more sense to store in HitTestResults
(which is the other half of MouseEventWithHitTestResults).  But after spending
some time looking into the details of implementing that it seems like it's
probably more work than just stuffing it here (there are still a lot of places
we pass a PlatformMouseEvent instead of a MouseEventWithHitTestResults).

So I'm OK with taking a bit of a short-cut here to make this CL more tractable. 
I think it's worth tracking with a comment here though, maybe something like:
"This might make more sense to put in HitTestResults or some other part of
MouseEventWithHitTestResults, but for now it's most convenient to stash it
here.".

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

Done.

I agree with you. I'll move the region data to HitTestResults or some other
parts in follow-up CL.
I left a comment and filed a bug for now.

[Rick Byers, 2016/03/08 15:57:34]

Thanks.  Note that I'm not convinced it's worth the effort / code churn to make
that change.  It would be nice to look into / experiment with, see if it's
practical to do cleanly without a TON of work.  But I don't consider it required
- storing it in PlatformMouseEvent isn't THAT bad, just a little bit of a hack.

 };
 
 } // namespace blink