Blink Support for Overlay Scrollbar Animation

Source/platform/scroll/Scrollbar.h

Index: Source/platform/scroll/Scrollbar.h
diff --git a/Source/platform/scroll/Scrollbar.h b/Source/platform/scroll/Scrollbar.h
index 0db0d3740f22d38c420e04dde9205b4dde88654a..aefdf7d62c54a311fd174379b4a569f1eb7e585e 100644
--- a/Source/platform/scroll/Scrollbar.h
+++ b/Source/platform/scroll/Scrollbar.h
@@ -30,6 +30,7 @@
 #include "platform/Widget.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
+#include "public/platform/WebThemeEngine.h"
 #include "wtf/MathExtras.h"
 #include "wtf/PassRefPtr.h"
 
@@ -101,6 +102,8 @@ public:
     // Called by the ScrollableArea when the scroll offset changes.
     void offsetDidChange();
 
+    void updateStateTransitionData(blink::WebThemeEngine::State, blink::WebThemeEngine::State, double);
+
     void disconnectFromScrollableArea() { m_scrollableArea = 0; }
     ScrollableArea* scrollableArea() const { return m_scrollableArea; }
 
@@ -117,6 +120,11 @@ public:
     virtual bool isOverlayScrollbar() const OVERRIDE;
     bool shouldParticipateInHitTesting();
 
+    virtual bool isDuringStateTransitionAnimation() const OVERRIDE;
+    virtual double stateTransitionProgress() const OVERRIDE;
+    virtual blink::WebThemeEngine::State stateTransitionStartState() const OVERRIDE;
+    virtual blink::WebThemeEngine::State stateTransitionEndState() const OVERRIDE;
+
     bool isWindowActive() const;
 
     bool gestureEvent(const PlatformGestureEvent&);
@@ -190,6 +198,10 @@ protected:
 
     bool m_isAlphaLocked;
 
+    double m_stateTransitionProgress;
+    blink::WebThemeEngine::State m_startState;
+    blink::WebThemeEngine::State m_endState;
+
 private:
     virtual bool isScrollbar() const OVERRIDE { return true; }