Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
index b60cfbcbfbea6ef5c5a60358ba6299897314ea72..9b1fb69267c52a13da0f04d73048b7b99bf13afe 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
@@ -72,6 +72,18 @@ bool ScrollbarThemeOverlay::usesOverlayScrollbars() const {
   return true;
 }
 
+double ScrollbarThemeOverlay::overlayScrollbarFadeOutDelaySeconds() const {
+  WebThemeEngine::ScrollbarStyle style;
+  Platform::current()->themeEngine()->getOverlayScrollbarStyle(&style);
+  return style.fadeOutDelaySeconds;
+}
+
+double ScrollbarThemeOverlay::overlayScrollbarFadeOutDurationSeconds() const {
+  WebThemeEngine::ScrollbarStyle style;
+  Platform::current()->themeEngine()->getOverlayScrollbarStyle(&style);
+  return style.fadeOutDurationSeconds;
+}
+
 int ScrollbarThemeOverlay::thumbPosition(const ScrollbarThemeClient& scrollbar,
                                          float scrollPosition) {
   if (!scrollbar.totalSize())
@@ -151,7 +163,10 @@ void ScrollbarThemeOverlay::paintThumb(GraphicsContext& context,
   }
 
   WebThemeEngine::State state = WebThemeEngine::StateNormal;
-  if (scrollbar.pressedPart() == ThumbPart)
+
+  if (!scrollbar.enabled())
+    state = WebThemeEngine::StateDisabled;
+  else if (scrollbar.pressedPart() == ThumbPart)
     state = WebThemeEngine::StatePressed;
   else if (scrollbar.hoveredPart() == ThumbPart)
     state = WebThemeEngine::StateHover;
@@ -177,7 +192,11 @@ ScrollbarPart ScrollbarThemeOverlay::hitTest(
   if (m_allowHitTest == DisallowHitTest)
     return NoPart;
 
-  return ScrollbarTheme::hitTest(scrollbar, position);
+  ScrollbarPart part = ScrollbarTheme::hitTest(scrollbar, position);
+  if (part != ThumbPart)
+    return NoPart;
+
+  return ThumbPart;
 }
 
 ScrollbarThemeOverlay& ScrollbarThemeOverlay::mobileTheme() {