Move ReferencedSurfaceTracker into GpuCompositorFrameSink.

services/ui/surfaces/display_compositor_unittest.cc

Index: services/ui/surfaces/display_compositor_unittest.cc
diff --git a/services/ui/surfaces/display_compositor_unittest.cc b/services/ui/surfaces/display_compositor_unittest.cc
index 6d2cf5a166dade018393196f7c815ff47ce23ad5..f7d21471fb9b7b42b7db3075cc965ab5c45f3c2e 100644
--- a/services/ui/surfaces/display_compositor_unittest.cc
+++ b/services/ui/surfaces/display_compositor_unittest.cc
@@ -67,20 +67,13 @@ class TestDisplayCompositorClient : public cc::mojom::DisplayCompositorClient {
   }
 
   // cc::mojom::DisplayCompositorClient:
-  void OnDisplayCompositorCreated(
-      const cc::SurfaceId& root_surface_id) override {
-    got_root_surface_id_ = true;
-  }
-
   void OnSurfaceCreated(const cc::SurfaceInfo& surface_info) override {
-    EXPECT_TRUE(got_root_surface_id_);
     AddEvent(base::StringPrintf("OnSurfaceCreated(%s)",
                                 SurfaceIdString(surface_info.id()).c_str()));
   }
 
   mojo::Binding<cc::mojom::DisplayCompositorClient> binding_;
   std::string events_;
-  bool got_root_surface_id_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(TestDisplayCompositorClient);
 };