[exp] cc: Introduce cc::CompositorMutator.

cc/layers/tiled_layer_unittest.cc

 // Copyright 2011 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/tiled_layer.h"
 
 #include <limits>
 #include <vector>
 
 #include "base/run_loop.h"
@@ skipping 77 matching lines @@
     settings_.layer_transforms_should_scale_layer_contents = true;
     settings_.verify_property_trees = true;
     settings_.impl_side_painting = false;
   }
 
   void SetUp() override {
     impl_thread_.Start();
     shared_bitmap_manager_.reset(new TestSharedBitmapManager());
     layer_tree_host_ = LayerTreeHost::CreateThreaded(
         &synchonous_output_surface_client_, shared_bitmap_manager_.get(),
-        nullptr, settings_, base::MessageLoopProxy::current(),
+        nullptr, nullptr, settings_, base::MessageLoopProxy::current(),
         impl_thread_.message_loop_proxy(), nullptr);
     synchonous_output_surface_client_.SetLayerTreeHost(layer_tree_host_.get());
     proxy_ = layer_tree_host_->proxy();
     resource_manager_ = PrioritizedResourceManager::Create(proxy_);
     layer_tree_host_->SetLayerTreeHostClientReady();
     CHECK(synchonous_output_surface_client_.EnsureOutputSurfaceCreated());
 
     layer_tree_host_->SetRootLayer(Layer::Create());
 
     CHECK(output_surface_->BindToClient(&output_surface_client_));
@@ skipping 1638 matching lines @@
 
   // Rounding leads to an extra pixel.
   gfx::Rect expanded_layer_rect(layer_rect);
   expanded_layer_rect.set_height(32);
   EXPECT_EQ(expanded_layer_rect,
             layer->tracking_layer_painter()->PaintedRect());
 }
 
 }  // namespace
 }  // namespace cc