Merge 182021 "Clip iframe overflow controls."

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
===================================================================
--- Source/core/rendering/compositing/RenderLayerCompositor.cpp	(revision 182215)
+++ Source/core/rendering/compositing/RenderLayerCompositor.cpp	(working copy)
@@ -488,6 +488,7 @@
     if (m_containerLayer) {
         FrameView* frameView = m_renderView.frameView();
         m_containerLayer->setSize(frameView->unscaledVisibleContentSize());
+        m_overflowControlsHostLayer->setSize(frameView->unscaledVisibleContentSize(IncludeScrollbars));
 
         frameViewDidScroll();
         updateOverflowControlsLayers();
@@ -712,6 +713,7 @@
     if (m_containerLayer) {
         FrameView* frameView = m_renderView.frameView();
         m_containerLayer->setSize(frameView->unscaledVisibleContentSize());
+        m_overflowControlsHostLayer->setSize(frameView->unscaledVisibleContentSize(IncludeScrollbars));
     }
 }
 
@@ -982,6 +984,7 @@
                 containerMasksToBounds = true;
         }
         m_containerLayer->setMasksToBounds(containerMasksToBounds);
+        m_overflowControlsHostLayer->setMasksToBounds(containerMasksToBounds);
 
         m_scrollLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())