Move viewport scrolling logic into separate class

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("//testing/test.gni")
 
 component("cc") {
   sources = [
     "animation/animation.cc",
     "animation/animation.h",
@@ skipping 211 matching lines @@
     "layers/ui_resource_layer.h",
     "layers/ui_resource_layer_impl.cc",
     "layers/ui_resource_layer_impl.h",
     "layers/video_frame_provider.h",
     "layers/video_frame_provider_client_impl.cc",
     "layers/video_frame_provider_client_impl.h",
     "layers/video_layer.cc",
     "layers/video_layer.h",
     "layers/video_layer_impl.cc",
     "layers/video_layer_impl.h",
+    "layers/viewport.cc",
+    "layers/viewport.h",
     "output/begin_frame_args.cc",
     "output/begin_frame_args.h",
     "output/bsp_tree.cc",
     "output/bsp_tree.h",
     "output/bsp_walk_action.cc",
     "output/bsp_walk_action.h",
     "output/compositor_frame.cc",
     "output/compositor_frame.h",
     "output/compositor_frame_ack.cc",
     "output/compositor_frame_ack.h",
@@ skipping 674 matching lines @@
     "//media",
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
     "//testing/perf",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gl",
   ]
 }