Clip iframe overflow controls.

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/compositing/RenderLayerCompositor.cpp b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
index 7355ed42f989715ca6c3e2965b591e988ef09d2d..61c78a42e94052d779db728d39c187f3b363aa69 100644
--- a/Source/core/rendering/compositing/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
@@ -493,6 +493,7 @@ void RenderLayerCompositor::frameViewDidChangeSize()
     if (m_containerLayer) {
         FrameView* frameView = m_renderView.frameView();
         m_containerLayer->setSize(frameView->unscaledVisibleContentSize());
+        m_overflowControlsHostLayer->setSize(frameView->unscaledVisibleContentSize(IncludeScrollbars));
 
         frameViewDidScroll();
         updateOverflowControlsLayers();
@@ -717,6 +718,7 @@ void RenderLayerCompositor::updateRootLayerPosition()
     if (m_containerLayer) {
         FrameView* frameView = m_renderView.frameView();
         m_containerLayer->setSize(frameView->unscaledVisibleContentSize());
+        m_overflowControlsHostLayer->setSize(frameView->unscaledVisibleContentSize(IncludeScrollbars));
     }
 }
 
@@ -987,6 +989,7 @@ void RenderLayerCompositor::ensureRootLayer()
                 containerMasksToBounds = true;
         }
         m_containerLayer->setMasksToBounds(containerMasksToBounds);
+        m_overflowControlsHostLayer->setMasksToBounds(containerMasksToBounds);
 
         m_scrollLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())