Implement MouseEvent buttons attribute.

Source/platform/PlatformMouseEvent.h

Index: Source/platform/PlatformMouseEvent.h
diff --git a/Source/platform/PlatformMouseEvent.h b/Source/platform/PlatformMouseEvent.h
index 488bd0c211c910e5137fe452603608f3484de634..bf95e7c5d5e59796fd939322b1f94aa901bb8e6f 100644
--- a/Source/platform/PlatformMouseEvent.h
+++ b/Source/platform/PlatformMouseEvent.h
@@ -95,6 +95,23 @@ public:
     bool fromTouch() const { return m_synthesized == FromTouch; }
     SyntheticEventType syntheticEventType() const { return m_synthesized; }
 
+    unsigned short buttons() const

[Rick Byers, 2014/11/18 20:29:19]

And actually, it doesn't really make sense for PlatformMouseEvent to expose the
buttons in two ways (via modifiers() and via buttons()) - especially when the
values (1, 2, 4) of the latter are really defined by the DOM event spec (i.e.
"4" has no definition here at the Platform layer - it's only within MouseEvent
that it makes sense to reference the DOM events spec).

So instead of modifying PlatformMouseEvent, please add a private function to
MouseEvent which converts a PlatformEvent::Modifiers value into a 'buttons'
value, and call it when creating MouseEvent objects from PlatformMouseEvent.

Sorry I didn't suggest this earlier.

[zino, 2014/11/24 13:07:08]

Done.

+    {
+        if (fromTouch())
+            return 1;

[Rick Byers, 2014/11/18 20:29:19]

This logic doesn't belong here, the caller should provide the correct modifiers
for touch scenarios.  In particular, for GestureLongPress we synthesize a
contextmenu event, which is a MouseEvent where buttons should be 2 (right mouse
button).  Please add a test for contextmenu with both mouse and GestureLongPress
input.

[zino, 2014/11/24 13:07:08]

Done.

[Rick Byers, 2014/11/25 17:44:27]

I still don't see why we should change the PlatformMouseEvent here for
'fromTouch' cases instead of just fixing the callers to supply the right
modifiers?  I think there are just three callers to be trivially updated:
EventHandler::HandleGestureTap, EventHandler::HandleGestureLongPress and
EventHandler::sendContextMenuEventForGesture.  That way PlatformMouseEvent will
reflect exactly the modifiers it's been given without mucking with them in any
way (we just adjust on the way in and way out as necessary).

[zino, 2014/11/28 02:37:07]

Here

[zino, 2014/11/28 12:29:28]

Done

+
+        unsigned short value = 0;
+
+        if (m_modifiers & LeftButtonDown)
+            value |= 1;
+        if (m_modifiers & RightButtonDown)
+            value |= 2;
+        if (m_modifiers & MiddleButtonDown)
+            value |= 4;
+
+        return value;
+    }
+
 protected:
     IntPoint m_position;
     IntPoint m_globalPosition;