Support high DPI scrollbar on top level web frame.

cc/CCLayerImpl.cpp

Index: cc/CCLayerImpl.cpp
diff --git a/cc/CCLayerImpl.cpp b/cc/CCLayerImpl.cpp
index 9068d31aaa6f76dab4e4af38643c0b6ec9595b77..c08b8604b0bb4d6a2fb36071238d317b311a4cb6 100644
--- a/cc/CCLayerImpl.cpp
+++ b/cc/CCLayerImpl.cpp
@@ -209,6 +209,15 @@ CCInputHandlerClient::ScrollStatus CCLayerImpl::tryScroll(const IntPoint& viewpo
     return CCInputHandlerClient::ScrollStarted;
 }
 
+IntRect CCLayerImpl::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);
+}
+
 std::string CCLayerImpl::indentString(int indent)
 {
     std::string str;