Support high DPI scrollbar on top level web frame.

cc/LayerChromium.cpp

Index: cc/LayerChromium.cpp
diff --git a/cc/LayerChromium.cpp b/cc/LayerChromium.cpp
index 59a63eff8e0db77d6557992b2e047f6dc01036ba..df5ea66bc9f9bd5f516acbae1c012c26eaad200d 100644
--- a/cc/LayerChromium.cpp
+++ b/cc/LayerChromium.cpp
@@ -116,6 +116,15 @@ void LayerChromium::setNeedsCommit()
         m_layerTreeHost->setNeedsCommit();
 }
 
+IntRect LayerChromium::layerRectToContentRect(const WebKit::WebRect& layerRect)
+{
+    float widthScale = static_cast<float>(contentBounds().width()) / bounds().width();
+    float heightScale = static_cast<float>(contentBounds().height()) / bounds().height();
+    FloatRect contentRect(layerRect.x, layerRect.y, layerRect.width, layerRect.height);
+    contentRect.scale(widthScale, heightScale);
+    return enclosingIntRect(contentRect);
+}
+
 void LayerChromium::setParent(LayerChromium* layer)
 {
     ASSERT(!layer || !layer->hasAncestor(this));