Implement MouseEvent buttons attribute.

Source/core/events/MouseEvent.h

Index: Source/core/events/MouseEvent.h
diff --git a/Source/core/events/MouseEvent.h b/Source/core/events/MouseEvent.h
index 7d77582ba2a91605fb24c8f314415a2610d5229b..4cf100b6d7cc0ceee026a18e09c8f0beeb6a4796 100644
--- a/Source/core/events/MouseEvent.h
+++ b/Source/core/events/MouseEvent.h
@@ -45,6 +45,7 @@ struct MouseEventInit : public UIEventInit {
     bool shiftKey;
     bool metaKey;
     unsigned short button;
+    unsigned short buttons;
     RefPtrWillBeMember<EventTarget> relatedTarget;
 };
 
@@ -59,7 +60,7 @@ public:
     static PassRefPtrWillBeRawPtr<MouseEvent> create(const AtomicString& type, bool canBubble, bool cancelable, PassRefPtrWillBeRawPtr<AbstractView>,
         int detail, int screenX, int screenY, int pageX, int pageY,
         int movementX, int movementY,
-        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short button,
+        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short button, unsigned modifiers,

[Rick Byers, 2014/11/25 17:44:28]

I don't think you want to require all callers of 'create' to use PlatformEvent's
notion of 'modifiers'.  For one, this makes the 'modifiers' argument redundant
with ctrlKey, altKey, etc.  But it's a bit of a layering problem for code that's
not using PlatformEvent at all (eg. synthetic events).

What I was thinking was that you'd leave all the constructor/create signatures
the same as you originally had them (eg. taking a 'buttons').  But change the
implementation in the couple places we create a MouseEvent from a
PlatformMouseEvent to also do the conversion from modifiers to buttons - similar
to how it already converts from modifiers to ctrlKey, altKey, etc.  I think this
is just two places: MouseEvent::create(..., PlatformMouseEvent, ...) and
WheelEventDispatchMediator::WheelEventDispatchMediator(const PlatformWheelEvent&
event, ...).

To avoid code duplication across these two places, you could add a protected
method on MouseEvent called 'platformEventModifiersToButtons' which you could
call from both places (if there's other uses, it's also fine for this to be
public).

Sorry I didn't explain this more thoroughly.  Does it make sense?

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

Done.

         PassRefPtrWillBeRawPtr<EventTarget> relatedTarget, PassRefPtrWillBeRawPtr<DataTransfer>,
         bool isSimulated = false, PlatformMouseEvent::SyntheticEventType = PlatformMouseEvent::RealOrIndistinguishable);
 
@@ -72,11 +73,12 @@ public:
     void initMouseEvent(const AtomicString& type, bool canBubble, bool cancelable, PassRefPtrWillBeRawPtr<AbstractView>,
         int detail, int screenX, int screenY, int clientX, int clientY,
         bool ctrlKey, bool altKey, bool shiftKey, bool metaKey,
-        unsigned short button, PassRefPtrWillBeRawPtr<EventTarget> relatedTarget);
+        unsigned short button, PassRefPtrWillBeRawPtr<EventTarget> relatedTarget, unsigned short buttons = 0);
 
     // WinIE uses 1,4,2 for left/middle/right but not for click (just for mousedown/up, maybe others),
     // but we will match the standard DOM.
     unsigned short button() const { return m_button; }
+    unsigned short buttons() const { return m_buttons; }
     bool buttonDown() const { return m_buttonDown; }
     EventTarget* relatedTarget() const { return m_relatedTarget.get(); }
     void setRelatedTarget(PassRefPtrWillBeRawPtr<EventTarget> relatedTarget) { m_relatedTarget = relatedTarget; }
@@ -100,7 +102,7 @@ protected:
     MouseEvent(const AtomicString& type, bool canBubble, bool cancelable, PassRefPtrWillBeRawPtr<AbstractView>,
         int detail, int screenX, int screenY, int pageX, int pageY,
         int movementX, int movementY,
-        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short button,
+        bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, unsigned short button, unsigned modifiers,
         PassRefPtrWillBeRawPtr<EventTarget> relatedTarget, PassRefPtrWillBeRawPtr<DataTransfer>,
         bool isSimulated, PlatformMouseEvent::SyntheticEventType);
 
@@ -109,7 +111,10 @@ protected:
     MouseEvent();
 
 private:
+    unsigned short modifiersToButtons(const AtomicString& type, unsigned short button, unsigned modifiers);
+
     unsigned short m_button;
+    unsigned short m_buttons;
     bool m_buttonDown;
     RefPtrWillBeMember<EventTarget> m_relatedTarget;
     RefPtrWillBeMember<DataTransfer> m_dataTransfer;