Disable clipping on root scroller's ancestors.

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

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h
index fbe3af31fe120941880ea97fa1b543c2c864fc25..98e6a4b96bd441d1373c437a312ca3882556afe8 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h
@@ -122,6 +122,7 @@ public:
     GraphicsLayer* frameScrollLayer() const;
     GraphicsLayer* scrollLayer() const;
     GraphicsLayer* containerLayer() const;
+    GraphicsLayer* rootContentLayer() const;
 
     enum RootLayerAttachment {
         RootLayerUnattached,
@@ -133,6 +134,12 @@ public:
     void updateRootLayerAttachment();
     void updateRootLayerPosition();
 
+    // If the root scroller isn't the root layer then the PaintLayerCompositor
+    // must disable clipping on its layers so that the root scroller can
+    // expand/shrink its clipping layer in response to top controls and have
+    // the result be visible.
+    void updateClippingOnCompositorLayers();
+
     void setIsInWindow(bool);
 
     static PaintLayerCompositor* frameContentsCompositor(LayoutPart*);