[exp] cc: Introduce cc::CompositorMutator.

cc/layers/picture_layer_unittest.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/layers/picture_layer.h"
 
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/picture_layer_impl.h"
 #include "cc/resources/resource_update_queue.h"
 #include "cc/test/fake_layer_tree_host.h"
@@ skipping 112 matching lines @@
   FakeLayerTreeHostClient host_client1(FakeLayerTreeHostClient::DIRECT_3D);
   FakeLayerTreeHostClient host_client2(FakeLayerTreeHostClient::DIRECT_3D);
   scoped_ptr<SharedBitmapManager> shared_bitmap_manager(
       new TestSharedBitmapManager());
 
   MockContentLayerClient client;
   scoped_refptr<FakePictureLayer> layer = FakePictureLayer::Create(&client);
 
   scoped_ptr<LayerTreeHost> host1 = LayerTreeHost::CreateSingleThreaded(
       &host_client1, &host_client1, shared_bitmap_manager.get(), nullptr,
-      settings, base::MessageLoopProxy::current(), nullptr);
+      nullptr, settings, base::MessageLoopProxy::current(), nullptr);
   host_client1.SetLayerTreeHost(host1.get());
 
   scoped_ptr<LayerTreeHost> host2 = LayerTreeHost::CreateSingleThreaded(
       &host_client2, &host_client2, shared_bitmap_manager.get(), nullptr,
-      settings, base::MessageLoopProxy::current(), nullptr);
+      nullptr, settings, base::MessageLoopProxy::current(), nullptr);
   host_client2.SetLayerTreeHost(host2.get());
 
   // The PictureLayer is put in one LayerTreeHost.
   host1->SetRootLayer(layer);
   // Do a main frame, record the picture layers.
   EXPECT_EQ(0u, layer->update_count());
   layer->SetNeedsDisplay();
   host1->Composite(base::TimeTicks::Now());
   EXPECT_EQ(1u, layer->update_count());
   EXPECT_EQ(1, host1->source_frame_number());
@@ skipping 11 matching lines @@
   // Do a main frame, record the picture layers. The frame number has changed
   // non-monotonically.
   layer->SetNeedsDisplay();
   host2->Composite(base::TimeTicks::Now());
   EXPECT_EQ(3u, layer->update_count());
   EXPECT_EQ(1, host2->source_frame_number());
 }
 
 }  // namespace
 }  // namespace cc