Make RootScroller set the outer viewport scroll layer in the compositor

cc/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 component("cc") {
   sources = [
     "animation/animation.cc",
@@ skipping 504 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 493 matching lines @@
     "//ui/gfx/geometry",
     "//ui/gl",
     "//ui/gl:test_support",
   ]
 
   # This target should not require the Chrome executable to run.
   assert_no_deps = [ "//chrome" ]
 }
 # When adding support for isolates, please have a look at run-time dependencies
 # in the cc_unittests_run target in cc_tests.gyp.