Removed a redundant mouse-state from EventHandler.

EventHandler currently have two state vars for tracking
node under mouse: m_nodeUnderMouse and m_lastNodeUnderMouse.
These two pointers are used primarily for mouse entry/exit
events, but they point to the same node until we are about
to send mouseenter/leave/over/out events. In the few cases
these pointers become unequal otherwise (happens only when
dispathMouseEvent is called with setUnder=false), it is not
clear why we didn't update the old state. My experiments
suggest that updating the old state doesn't hurt in these
cases. So it makes sense to nuke the m_lastNodeUnderMouse
state.

BUG=

Review URL: https://codereview.chromium.org/1293973004

git-svn-id: svn://svn.chromium.org/blink/trunk@201023 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/input/EventHandler.h

@@ -279,14 +279,14 @@ private:
 
     void invalidateClick();
 
-    void updateMouseEventTargetNode(Node*, const PlatformMouseEvent&, bool);
+    void updateMouseEventTargetNode(Node*, const PlatformMouseEvent&);
 
     /* Dispatches mouseover, mouseout, mouseenter and mouseleave events to appropriate nodes when the mouse pointer moves from one node to another. */
     void sendMouseEventsForNodeTransition(Node*, Node*, const PlatformMouseEvent&);
 
     MouseEventWithHitTestResults prepareMouseEvent(const HitTestRequest&, const PlatformMouseEvent&);
 
-    bool dispatchMouseEvent(const AtomicString& eventType, Node* target, int clickCount, const PlatformMouseEvent&, bool setUnder);
+    bool dispatchMouseEvent(const AtomicString& eventType, Node* target, int clickCount, const PlatformMouseEvent&);
     bool dispatchDragEvent(const AtomicString& eventType, Node* target, const PlatformMouseEvent&, DataTransfer*);
 
     void clearDragDataTransfer();
@@ -372,7 +372,6 @@ private:
     bool m_eventHandlerWillResetCapturingMouseEventsNode;
 
     RefPtrWillBeMember<Node> m_nodeUnderMouse;
-    RefPtrWillBeMember<Node> m_lastNodeUnderMouse;
     RefPtrWillBeMember<LocalFrame> m_lastMouseMoveEventSubframe;
     RefPtrWillBeMember<Scrollbar> m_lastScrollbarUnderMouse;