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

mojo/examples/compositor_app/compositor_host.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 "mojo/examples/compositor_app/compositor_host.h"
 
 #include "cc/layers/layer.h"
 #include "cc/layers/solid_color_layer.h"
 #include "cc/output/context_provider.h"
 #include "cc/output/output_surface.h"
@@ skipping 90 matching lines @@
   static const double kDegreesPerSecond = 70.0;
   double child_rotation_degrees = kDegreesPerSecond * frame_begin_time;
   gfx::Transform child_transform;
   child_transform.Translate(200, 200);
   child_transform.Rotate(child_rotation_degrees);
   child_layer_->SetTransform(child_transform);
   tree_->SetNeedsAnimate();
 }
 
 void CompositorHost::Layout() {}
-void CompositorHost::ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+void CompositorHost::ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                          float page_scale) {}
 
 scoped_ptr<cc::OutputSurface> CompositorHost::CreateOutputSurface(
     bool fallback) {
   return make_scoped_ptr(
       new cc::OutputSurface(new MojoContextProvider(gles2_client_impl_)));
 }
 
 void CompositorHost::DidInitializeOutputSurface(bool success) {}
 
 void CompositorHost::WillCommit() {}
 void CompositorHost::DidCommit() {}
 void CompositorHost::DidCommitAndDrawFrame() {}
 void CompositorHost::DidCompleteSwapBuffers() {}
 
 scoped_refptr<cc::ContextProvider> CompositorHost::OffscreenContextProvider() {
   return NULL;
 }
 
 }  // namespace examples
 }  // namespace mojo