Make RootScroller set the outer viewport scroll layer in the compositor

cc/cc.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 565 matching lines @@
         'trees/proxy_common.h',
         'trees/proxy_impl.cc',
         'trees/proxy_impl.h',
         'trees/proxy_main.cc',
         'trees/proxy_main.h',
         'trees/remote_channel_impl.cc',
         'trees/remote_channel_impl.h',
         'trees/remote_channel_main.cc',
         'trees/remote_channel_main.h',
         'trees/remote_proto_channel.h',
+        'trees/root_scroller_controller.cc',
+        'trees/root_scroller_controller.h',
         'trees/scoped_abort_remaining_swap_promises.h',
         'trees/single_thread_proxy.cc',
         'trees/single_thread_proxy.h',
         'trees/swap_promise_monitor.cc',
         'trees/swap_promise_monitor.h',
         'trees/task_runner_provider.cc',
         'trees/task_runner_provider.h',
         'trees/threaded_channel.cc',
         'trees/threaded_channel.h',
         'trees/tree_synchronizer.cc',
@@ skipping 107 matching lines @@
         'surfaces/surface_resource_holder.h',
         'surfaces/surface_sequence.h',
         'surfaces/surfaces_export.h',
       ],
       'includes': [
         '../build/android/increase_size_for_speed.gypi',
       ],
     },
   ],
 }