[Slimming Paint] Paint the inspector overlay with GraphicsLayer DisplayList.

Source/web/PageOverlayList.h

Index: Source/web/PageOverlayList.h
diff --git a/Source/web/PageOverlayList.h b/Source/web/PageOverlayList.h
index 779a7db74d9a4d4bf90b5b475a07e656f639c1db..f321965efcd04d3176fd1fd299b071e7301f159d 100644
--- a/Source/web/PageOverlayList.h
+++ b/Source/web/PageOverlayList.h
@@ -59,6 +59,11 @@ public:
 
     size_t findGraphicsLayer(GraphicsLayer*);
 
+    // FIXME: Really, it should be possible for there to be multiple.
+    // But the signature of WebViewImpl::setOverlayLayer already seems to
+    // preclude that.
+    GraphicsLayer* graphicsLayerForTesting() const;
+
 private:
     typedef Vector<OwnPtr<PageOverlay>, 2> PageOverlays;