Use a struct for cc::Surface ids for more type safety

cc/surfaces/surface_aggregator_test_helpers.h

 // Copyright 2014 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.
 
 #ifndef CC_SURFACES_SURFACE_AGGREGATOR_TEST_HELPERS_H_
 #define CC_SURFACES_SURFACE_AGGREGATOR_TEST_HELPERS_H_
 
 #include "cc/quads/draw_quad.h"
 #include "cc/quads/render_pass.h"
+#include "cc/surfaces/surface_id.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/size.h"
 
 namespace cc {
 
 class Surface;
 class TestRenderPass;
 
 namespace test {
 
 struct Quad {
   static Quad SolidColorQuad(SkColor color) {
     Quad quad;
     quad.material = DrawQuad::SOLID_COLOR;
     quad.color = color;
     return quad;
   }
 
-  static Quad SurfaceQuad(int surface_id) {
+  static Quad SurfaceQuad(SurfaceId surface_id) {
     Quad quad;
     quad.material = DrawQuad::SURFACE_CONTENT;
     quad.surface_id = surface_id;
     return quad;
   }
 
   static Quad RenderPassQuad(RenderPass::Id id) {
     Quad quad;
     quad.material = DrawQuad::RENDER_PASS;
     quad.render_pass_id = id;
     return quad;
   }
 
   DrawQuad::Material material;
   // Set when material==DrawQuad::SURFACE_CONTENT.
-  int surface_id;
+  SurfaceId surface_id;
   // Set when material==DrawQuad::SOLID_COLOR.
   SkColor color;
   // Set when material==DrawQuad::RENDER_PASS.
   RenderPass::Id render_pass_id;
 
  private:
   Quad()
       : material(DrawQuad::INVALID),
-        surface_id(-1),
         color(SK_ColorWHITE),
         render_pass_id(-1, -1) {}
 };
 
 struct Pass {
   Pass(Quad* quads, size_t quad_count, RenderPass::Id id)
       : quads(quads), quad_count(quad_count), id(id) {}
   Pass(Quad* quads, size_t quad_count)
       : quads(quads), quad_count(quad_count), id(1, 1) {}
 
@@ skipping 22 matching lines @@
                                  RenderPassList* passes);
 
 void SubmitFrame(Pass* passes, size_t pass_count, Surface* surface);
 
 void QueuePassAsFrame(scoped_ptr<RenderPass> pass, Surface* surface);
 
 }  // namespace test
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_AGGREGATOR_TEST_HELPERS_H_