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

cc/layers/heads_up_display_layer.cc

Index: cc/layers/heads_up_display_layer.cc
diff --git a/cc/layers/heads_up_display_layer.cc b/cc/layers/heads_up_display_layer.cc
index 92486cc851599a7b7a7b7bd7c4b3a741d4fd9dfa..ca63471e303d9a97271e2d280d2c4f6abbc5ea9e 100644
--- a/cc/layers/heads_up_display_layer.cc
+++ b/cc/layers/heads_up_display_layer.cc
@@ -21,7 +21,7 @@ HeadsUpDisplayLayer::HeadsUpDisplayLayer() {}
 HeadsUpDisplayLayer::~HeadsUpDisplayLayer() {}
 
 void HeadsUpDisplayLayer::PrepareForCalculateDrawProperties(
-    gfx::Size device_viewport, float device_scale_factor) {
+    const gfx::Size& device_viewport, float device_scale_factor) {
   gfx::Size device_viewport_in_layout_pixels = gfx::Size(
       device_viewport.width() / device_scale_factor,
       device_viewport.height() / device_scale_factor);