[#7] Pass gfx structs by const ref (gfx::Size)

cc/layers/delegated_renderer_layer.h

Index: cc/layers/delegated_renderer_layer.h
diff --git a/cc/layers/delegated_renderer_layer.h b/cc/layers/delegated_renderer_layer.h
index dc9dfee47055ed1dd1361b4a0df65d8621c045f4..a0b67dfccf67bf5dbad66a47e2d64e46b1f177ca 100644
--- a/cc/layers/delegated_renderer_layer.h
+++ b/cc/layers/delegated_renderer_layer.h
@@ -33,7 +33,7 @@ class CC_EXPORT DelegatedRendererLayer : public Layer {
   // layer's origin. This must always contain at least the layer's bounds. A
   // value of (0, 0) implies that the frame should be displayed to fit exactly
   // in the layer's bounds.
-  void SetDisplaySize(gfx::Size size);
+  void SetDisplaySize(const gfx::Size& size);
 
   // Called by the DelegatedFrameProvider when a new frame is available to be
   // picked up.