Populates sourceDevice attribute into MouseEvent

Source/core/events/MouseRelatedEvent.h

Index: Source/core/events/MouseRelatedEvent.h
diff --git a/Source/core/events/MouseRelatedEvent.h b/Source/core/events/MouseRelatedEvent.h
index 6b4ae753e08e1ab1ac95a98cb7c79c0bf42bcb29..df644cf772b1cd330fc2a98cdc0596bb0ba5934e 100644
--- a/Source/core/events/MouseRelatedEvent.h
+++ b/Source/core/events/MouseRelatedEvent.h
@@ -68,7 +68,7 @@ namespace blink {
         MouseRelatedEvent(const AtomicString& type, bool canBubble, bool cancelable,
             PassRefPtrWillBeRawPtr<AbstractView>, int detail, const IntPoint& screenLocation,
             const IntPoint& rootFrameLocation, const IntPoint& movementDelta, bool ctrlKey, bool altKey,
-            bool shiftKey, bool metaKey, bool isSimulated = false);
+            bool shiftKey, bool metaKey, bool isSimulated = false, InputDevice* sourceDevice = nullptr);

[Rick Byers, 2015/06/25 03:34:54]

nit: as discussed offline, default InputDevice values like this are probably
dangerous (make it too easy for a caller to accidentally forget to provide an
InputDevice - if it should be nullptr then ideally that would be explicit at the
call site).  Feel free to just add a "TODO: make this argument non-optional"
comment for now.

[lanwei, 2015/06/25 19:26:40]

Done.

 
         void initCoordinates();
         void initCoordinates(const LayoutPoint& clientLocation);