For SPv2, attach element to compositor animation player without a CLM.

third_party/WebKit/Source/core/animation/CompositorAnimations.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 426 matching lines @@
 }
 
 void CompositorAnimations::attachCompositedLayers(Element& element,
                                                   const Animation& animation) {
   if (!animation.compositorPlayer())
     return;
 
   if (!element.layoutObject() || !element.layoutObject()->isBoxModelObject())
     return;
 
-  PaintLayer* layer = toLayoutBoxModelObject(element.layoutObject())->layer();
+  // Composited animations do not depend on a composited layer mapping for SPv2.
+  if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
+    PaintLayer* layer = toLayoutBoxModelObject(element.layoutObject())->layer();
 
-  if (!layer || !layer->isAllowedToQueryCompositingState() ||
-      !layer->compositedLayerMapping() ||
-      !layer->compositedLayerMapping()->mainGraphicsLayer())
-    return;
+    if (!layer || !layer->isAllowedToQueryCompositingState() ||
+        !layer->compositedLayerMapping() ||
+        !layer->compositedLayerMapping()->mainGraphicsLayer())
+      return;
 
-  if (!layer->compositedLayerMapping()->mainGraphicsLayer()->platformLayer())
-    return;
+    if (!layer->compositedLayerMapping()->mainGraphicsLayer()->platformLayer())
+      return;
+  }
 
   CompositorAnimationPlayer* compositorPlayer = animation.compositorPlayer();
   compositorPlayer->attachElement(createCompositorElementId(

[wkorman, 2017/01/20 23:45:47]

This will end up at this check:

 
https://cs.chromium.org/chromium/src/cc/animation/animation_player.cc?q=anima...

  if (animation_host_)
      RegisterPlayer();

I'm not yet sure whether animation_host_ will be true when we need it to be.
Further changes may be needed but this seems an incremental step with what I
know currently.

[loyso (OOO), 2017/01/24 00:48:20]

cc::AnimationPlayer::animation_host_ is not nullptr if
1) Player is added to timeline
2) Timeline is added to AnimationHost.

       DOMNodeIds::idForNode(&element), CompositorSubElementId::Primary));
 }
 
 bool CompositorAnimations::convertTimingForCompositor(
     const Timing& timing,
     double timeOffset,
     CompositorTiming& out,
     double animationPlaybackRate) {
   timing.assertValid();
 
@@ skipping 167 matching lines @@
     animation->setTimeOffset(compositorTiming.scaledTimeOffset);
     animation->setDirection(compositorTiming.direction);
     animation->setPlaybackRate(compositorTiming.playbackRate);
     animation->setFillMode(compositorTiming.fillMode);
     animations.push_back(std::move(animation));
   }
   DCHECK(!animations.isEmpty());
 }
 
 }  // namespace blink