Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
index 6d1f93cb3929f5fc1fb886b2e56d0111ea195f17..448ce5aa8019855de0e879973a83435f6f7ddef5 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -658,6 +658,8 @@ void PaintLayerCompositor::frameViewDidScroll() {
   else
     m_scrollLayer->setPosition(IntPoint(-scrollOffset));
 
+  showScrollbarLayersIfNeeded();
+
   DEFINE_STATIC_LOCAL(EnumerationHistogram, acceleratedBackgroundHistogram,
                       ("Renderer.AcceleratedFixedRootBackground",
                        AcceleratedFixedRootBackgroundHistogramMax));
@@ -1087,6 +1089,15 @@ void PaintLayerCompositor::updateOverflowControlsLayers() {
   }
 
   m_layoutView.frameView()->positionScrollbarLayers();
+  showScrollbarLayersIfNeeded();
+}
+
+void PaintLayerCompositor::showScrollbarLayersIfNeeded() {
+  FrameView* frameView = m_layoutView.frameView();
+  if (m_scrollLayer && frameView->needsShowScrollbarLayers()) {
+    m_scrollLayer->platformLayer()->showScrollbars();
+    frameView->didShowScrollbarLayers();
+  }
 }
 
 void PaintLayerCompositor::ensureRootLayer() {