Added a CallbackLayerAnimationObserver.

ui/compositor/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("compositor") {
   sources = [
+    "callback_layer_animation_observer.cc",
+    "callback_layer_animation_observer.h",
     "canvas_painter.cc",
     "canvas_painter.h",
     "clip_transform_recorder.cc",
     "clip_transform_recorder.h",
     "closure_animation_observer.cc",
     "closure_animation_observer.h",
     "compositing_recorder.cc",
     "compositing_recorder.h",
     "compositor.cc",
     "compositor.h",
@@ skipping 75 matching lines @@
   testonly = true
   sources = [
     "test/context_factories_for_test.cc",
     "test/context_factories_for_test.h",
     "test/draw_waiter_for_test.cc",
     "test/draw_waiter_for_test.h",
     "test/in_process_context_factory.cc",
     "test/in_process_context_factory.h",
     "test/in_process_context_provider.cc",
     "test/in_process_context_provider.h",
+    "test/layer_animation_observer_test_api.cc",
+    "test/layer_animation_observer_test_api.h",
     "test/layer_animator_test_controller.cc",
     "test/layer_animator_test_controller.h",
     "test/test_compositor_host.h",
     "test/test_compositor_host_mac.mm",
     "test/test_compositor_host_win.cc",
     "test/test_layer_animation_delegate.cc",
     "test/test_layer_animation_delegate.h",
     "test/test_layer_animation_observer.cc",
     "test/test_layer_animation_observer.h",
     "test/test_layers.cc",
@@ skipping 42 matching lines @@
   # The _run targets exist only for compatibility w/ GYP.
   group("compositor_unittests_run") {
     testonly = true
     deps = [
       ":compositor_unittests",
     ]
   }
 
   test("compositor_unittests") {
     sources = [
+      "callback_layer_animation_observer_unittest.cc",
       "compositor_unittest.cc",
       "layer_animation_element_unittest.cc",
       "layer_animation_sequence_unittest.cc",
       "layer_animator_unittest.cc",
       "layer_owner_unittest.cc",
       "layer_unittest.cc",
       "run_all_unittests.cc",
       "transform_animation_curve_adapter_unittest.cc",
     ]
 
@@ skipping 17 matching lines @@
       "//ui/gfx/geometry",
       "//ui/gl",
       "//ui/resources",
     ]
 
     if (is_linux) {
       deps += [ "//third_party/mesa:osmesa" ]
     }
   }
 }