Blink Support for Overlay Scrollbar Animation

Source/platform/scroll/ScrollableArea.cpp

Index: Source/platform/scroll/ScrollableArea.cpp
diff --git a/Source/platform/scroll/ScrollableArea.cpp b/Source/platform/scroll/ScrollableArea.cpp
index 39ad11ff0d74438e7263719b0dc0e2d76f09fd69..d08622bac6f3295c78a1596227c85045a64f67db 100644
--- a/Source/platform/scroll/ScrollableArea.cpp
+++ b/Source/platform/scroll/ScrollableArea.cpp
@@ -32,12 +32,13 @@
 #include "config.h"
 #include "platform/scroll/ScrollableArea.h"
 
+#include "platform/TraceEvent.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/geometry/FloatPoint.h"
+#include "platform/scroll/ScrollbarStateTransitionAnimator.h"
 #include "platform/scroll/ScrollbarTheme.h"
 #include "wtf/PassOwnPtr.h"
 
-#include "platform/TraceEvent.h"
 
 static const int kPixelsPerLineStep = 40;
 static const float kMinFractionToStepWhenPaging = 0.875f;
@@ -49,6 +50,7 @@ struct SameSizeAsScrollableArea {
     unsigned damageBits : 2;
     IntRect scrollbarDamage[2];
     void* pointer;
+    void* stateTranstionAnimatorPointer;

[abarth-chromium, 2014/06/16 22:47:04]

The point of having this struct here is to keep the size of this struct small. 
Is this feature worth the boat to this datastructure?

     unsigned bitfields : 16;
     IntPoint origin;
 };
@@ -95,6 +97,36 @@ ScrollAnimator* ScrollableArea::scrollAnimator() const
     return m_scrollAnimator.get();
 }
 
+ScrollbarStateTransitionAnimator* ScrollableArea::scrollbarStateTransitionAnimator() const
+{
+    if (hasOverlayScrollbars() && !m_scrollbarStateTransitionAnimator)
+        m_scrollbarStateTransitionAnimator = ScrollbarStateTransitionAnimator::create(const_cast<ScrollableArea*>(this));
+
+    return m_scrollbarStateTransitionAnimator.get();
+}
+
+bool ScrollableArea::isDuringStateTransitionAnimation() const
+{
+    return hasOverlayScrollbars() && existingScrollbarStateTransitionAnimator() && existingScrollbarStateTransitionAnimator()->isDuringStateTransitionAnimation();
+}
+
+void ScrollableArea::stateTransitionInProgress()
+{
+    if (isDuringStateTransitionAnimation()) {
+        double progress = existingScrollbarStateTransitionAnimator()->stateTransitionProgress();
+        blink::WebThemeEngine::State startState = existingScrollbarStateTransitionAnimator()->stateTransitionStartState();
+        blink::WebThemeEngine::State endState = existingScrollbarStateTransitionAnimator()->stateTransitionEndState();
+
+        if (Scrollbar* verticalScrollbar = this->verticalScrollbar()) {
+            verticalScrollbar->updateStateTransitionData(startState, endState, progress);
+        }
+
+        if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar()) {
+            horizontalScrollbar->updateStateTransitionData(startState, endState, progress);
+        }
+    }
+}
+
 void ScrollableArea::setScrollOrigin(const IntPoint& origin)
 {
     if (m_scrollOrigin != origin) {
@@ -276,11 +308,15 @@ void ScrollableArea::mouseMovedInContentArea() const
 void ScrollableArea::mouseEnteredScrollbar(Scrollbar* scrollbar) const
 {
     scrollAnimator()->mouseEnteredScrollbar(scrollbar);
+    if (ScrollbarStateTransitionAnimator* animator = scrollbarStateTransitionAnimator())
+        animator->mouseEnteredScrollbar(scrollbar);
 }
 
 void ScrollableArea::mouseExitedScrollbar(Scrollbar* scrollbar) const
 {
     scrollAnimator()->mouseExitedScrollbar(scrollbar);
+    if (ScrollbarStateTransitionAnimator* animator = scrollbarStateTransitionAnimator())
+        animator->mouseExitedScrollbar(scrollbar);
 }
 
 void ScrollableArea::contentAreaDidShow() const
@@ -392,10 +428,12 @@ bool ScrollableArea::hasLayerForScrollCorner() const
     return layerForScrollCorner();
 }
 
-void ScrollableArea::serviceScrollAnimations()
+void ScrollableArea::serviceScrollbarAnimations()
 {
     if (ScrollAnimator* scrollAnimator = existingScrollAnimator())
         scrollAnimator->serviceScrollAnimations();
+    if (ScrollbarStateTransitionAnimator* animator = existingScrollbarStateTransitionAnimator())
+        animator->serviceAnimations();
 }
 
 IntRect ScrollableArea::visibleContentRect(IncludeScrollbarsInRect scrollbarInclusion) const