[#7] Pass gfx::Size by const ref.

Any struct of size > 4 bytes should be passed by const ref. 
Passing by ref for these structs is faster than passing by value,
especially when invoking function has multiple parameters and some
other scenarios mentioned in the bug.

BUG=159273

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247426

Review URL: https://codereview.chromium.org/145313006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247769 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/cc/test/pixel_test.h b/cc/test/pixel_test.h
index b6e02422..6d5c552 100644
--- a/cc/test/pixel_test.h
+++ b/cc/test/pixel_test.h
@@ -59,7 +59,7 @@
   void SetUpGLRenderer(bool use_skia_gpu_backend);
   void SetUpSoftwareRenderer();
 
-  void ForceExpandedViewport(gfx::Size surface_expansion);
+  void ForceExpandedViewport(const gfx::Size& surface_expansion);
   void ForceViewportOffset(gfx::Vector2d viewport_offset);
   void ForceDeviceClip(const gfx::Rect& clip);
   void EnableExternalStencilTest();