[DevTools] Use device metrics emulation implemented in content.

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index 1ea9f0d6cac234fff5d3b12110d82d54db11b137..a9d0b18b44cb9043f88c46c8afbf199953a32729 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -2434,10 +2434,14 @@ void RenderLayerCompositor::ensureRootLayer()
         // Create a layer to host the clipping layer and the overflow controls layers.
         m_overflowControlsHostLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 
-        // Create a clipping layer if this is an iframe
+        // Create a clipping layer if this is an iframe or settings require to clip.
         m_containerLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
-        if (!isMainFrame())
-            m_containerLayer->setMasksToBounds(true);
+        bool containerMasksToBounds = !isMainFrame();
+        if (Settings* settings = m_renderView->document().settings()) {
+            if (settings->mainFrameClipsContent())
+                containerMasksToBounds = true;
+        }
+        m_containerLayer->setMasksToBounds(containerMasksToBounds);
 
         m_scrollLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())