CC Animations: Allow timelines and players without host to support non-compositingMode

cc/animation/animation_timeline.cc

 // Copyright 2015 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.
 
 #include "cc/animation/animation_timeline.h"
 
 #include <algorithm>
 
 #include "cc/animation/animation_player.h"
 
@@ skipping 17 matching lines @@
   return timeline;
 }
 
 void AnimationTimeline::SetAnimationHost(AnimationHost* animation_host) {
   animation_host_ = animation_host;
   for (auto& player : players_)
     player->SetAnimationHost(animation_host);
 }
 
 void AnimationTimeline::AttachPlayer(scoped_refptr<AnimationPlayer> player) {
-  DCHECK(animation_host_);
   player->SetAnimationHost(animation_host_);
+
   player->SetAnimationTimeline(this);
   players_.push_back(player);
 }
 
 void AnimationTimeline::DetachPlayer(scoped_refptr<AnimationPlayer> player) {
   for (AnimationPlayerList::iterator iter = players_.begin();
        iter != players_.end(); ++iter) {
     if (iter->get() != player)
       continue;
 
@@ skipping 61 matching lines @@
 void AnimationTimeline::PushPropertiesToImplThread(
     AnimationTimeline* timeline_impl) {
   for (auto& player : players_) {
     AnimationPlayer* player_impl = timeline_impl->GetPlayerById(player->id());
     if (player_impl)
       player->PushPropertiesTo(player_impl);
   }
 }
 
 }  // namespace cc