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

cc/test/pixel_test.cc

Index: cc/test/pixel_test.cc
diff --git a/cc/test/pixel_test.cc b/cc/test/pixel_test.cc
index e84540e3ed424dd773a5cc32828a0fcbd86f5dee..1257be6b61d4d2445c793b951a1c48bd401a2328 100644
--- a/cc/test/pixel_test.cc
+++ b/cc/test/pixel_test.cc
@@ -137,7 +137,7 @@
                                  0).PassAs<DirectRenderer>();
 }
 
-void PixelTest::ForceExpandedViewport(const gfx::Size& surface_expansion) {
+void PixelTest::ForceExpandedViewport(gfx::Size surface_expansion) {
   static_cast<PixelTestOutputSurface*>(output_surface_.get())
       ->set_surface_expansion_size(surface_expansion);
   SoftwareOutputDevice* device = output_surface_->software_device();