[exp] cc: Introduce cc::CompositorMutator.

content/test/web_layer_tree_view_impl_for_testing.cc

Index: content/test/web_layer_tree_view_impl_for_testing.cc
diff --git a/content/test/web_layer_tree_view_impl_for_testing.cc b/content/test/web_layer_tree_view_impl_for_testing.cc
index fb77dc15b5f98f4b57a27bc83f020a1c88cdb824..20da3cd6208d63dcb76119b2bcde30dd5b60cc22 100644
--- a/content/test/web_layer_tree_view_impl_for_testing.cc
+++ b/content/test/web_layer_tree_view_impl_for_testing.cc
@@ -44,13 +44,8 @@ void WebLayerTreeViewImplForTesting::Initialize() {
   // Accelerated animations are enabled for unit tests.
   settings.accelerated_animation_enabled = true;
   layer_tree_host_ = cc::LayerTreeHost::CreateSingleThreaded(
-      this,
-      this,
-      nullptr,
-      nullptr,
-      settings,
-      base::MessageLoopProxy::current(),
-      nullptr);
+      this, this, nullptr, nullptr, nullptr, settings,
+      base::MessageLoopProxy::current(), nullptr);
   DCHECK(layer_tree_host_);
 }