NOT FOR REVIEW - convert to cc animation

cc/animation/BUILD.gn

 # Copyright 2016 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("//cc/cc.gni")
 
 cc_component("animation") {
   output_name = "cc_animation"
   sources = [
     "animation.cc",
     "animation.h",
     "animation_curve.cc",
     "animation_curve.h",
     "animation_delegate.h",
     "animation_events.cc",
     "animation_events.h",
     "animation_export.h",
     "animation_host.cc",
     "animation_host.h",
     "animation_id_provider.cc",
     "animation_id_provider.h",
+    "animation_observer.h",
     "animation_player.cc",
     "animation_player.h",
     "animation_timeline.cc",
     "animation_timeline.h",
     "element_animations.cc",
     "element_animations.h",
     "keyframed_animation_curve.cc",
     "keyframed_animation_curve.h",
     "scroll_offset_animation_curve.cc",
     "scroll_offset_animation_curve.h",
@@ skipping 11 matching lines @@
 
   defines = [ "CC_ANIMATION_IMPLEMENTATION=1" ]
 
   deps = [
     "//base",
     "//cc",
     "//ui/gfx",
     "//ui/gfx/geometry",
   ]
 }