[#6]Pass gfx structs by const ref (gfx::Vector2d)

cc/test/pixel_test.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/test/pixel_test.h"
 
 #include "base/command_line.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "cc/base/switches.h"
@@ skipping 129 matching lines @@
 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();
   if (device) {
     static_cast<PixelTestSoftwareOutputDevice*>(device)
         ->set_surface_expansion_size(surface_expansion);
   }
 }
 
-void PixelTest::ForceViewportOffset(gfx::Vector2d viewport_offset) {
+void PixelTest::ForceViewportOffset(const gfx::Vector2d& viewport_offset) {
   external_device_viewport_offset_ = viewport_offset;
 }
 
 void PixelTest::ForceDeviceClip(const gfx::Rect& clip) {
   external_device_clip_rect_ = clip;
 }
 
 void PixelTest::EnableExternalStencilTest() {
   static_cast<PixelTestOutputSurface*>(output_surface_.get())
       ->set_has_external_stencil_test(true);
 }
 
 void PixelTest::SetUpSoftwareRenderer() {
   scoped_ptr<SoftwareOutputDevice> device(new PixelTestSoftwareOutputDevice());
   output_surface_.reset(new PixelTestOutputSurface(device.Pass()));
   output_surface_->BindToClient(output_surface_client_.get());
   resource_provider_ =
       ResourceProvider::Create(output_surface_.get(), NULL, 0, false, 1);
   renderer_ = SoftwareRenderer::Create(
       this, &settings_, output_surface_.get(), resource_provider_.get())
                   .PassAs<DirectRenderer>();
 }
 
 }  // namespace cc