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 1f2c9789647ab2ca8b178eab32df34cb5b50cae2..8eb10a6dd3aaac6a8994f89f4562cef83bdff8a7 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -649,6 +649,8 @@ void PaintLayerCompositor::frameViewDidScroll() {
   else
     m_scrollLayer->setPosition(IntPoint(-scrollOffset));
 
+  showScrollbarLayersIfNeeded();
+
   DEFINE_STATIC_LOCAL(EnumerationHistogram, acceleratedBackgroundHistogram,
                       ("Renderer.AcceleratedFixedRootBackground",
                        AcceleratedFixedRootBackgroundHistogramMax));
@@ -1078,6 +1080,15 @@ 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() {