[SPv1] Always set a CompositorElementId on main graphics layers; use PaintLayer id.

third_party/WebKit/Source/core/animation/Animation.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 25 matching lines @@
 #include "core/animation/css/CSSAnimations.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/StyleChangeReason.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/events/AnimationPlaybackEvent.h"
 #include "core/frame/UseCounter.h"
 #include "core/inspector/InspectorTraceEvents.h"
+#include "core/paint/PaintLayer.h"
 #include "core/probe/CoreProbes.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/ScriptForbiddenScope.h"
 #include "platform/WebTaskRunner.h"
 #include "platform/animation/CompositorAnimationPlayer.h"
 #include "platform/heap/Persistent.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 #include "platform/wtf/MathExtras.h"
 #include "platform/wtf/PtrUtil.h"
 #include "public/platform/Platform.h"
@@ skipping 689 matching lines @@
 
   // If the optional element id set has no value we must be in SPv1 mode in
   // which case we trust the compositing logic will create a layer if needed.
   if (composited_element_ids.has_value()) {
     DCHECK(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
     Element* target_element =
         ToKeyframeEffectReadOnly(content_.Get())->Target();
     if (!target_element)
       return false;
 
-    CompositorElementId target_element_id = CompositorElementIdFromDOMNodeId(
-        DOMNodeIds::IdForNode(target_element),
-        CompositorElementIdNamespace::kPrimary);
-    if (!composited_element_ids->Contains(target_element_id))
+    if (target_element->GetLayoutObject() &&

[wkorman, 2017/05/18 00:45:58]

nit: pulling target_element->GetLayoutObject() into local var above can shorten
4 refs here and below

+        target_element->GetLayoutObject()->IsBoxModelObject() &&
+        target_element->GetLayoutObject()->HasLayer()) {
+      PaintLayer* paint_layer =
+          ToLayoutBoxModelObject(target_element->GetLayoutObject())->Layer();
+      CompositorElementId target_element_id =
+          CompositorElementIdFromPaintLayerId(
+              paint_layer->UniqueId(), CompositorElementIdNamespace::kPrimary);
+      if (!composited_element_ids->Contains(target_element_id))
+        return false;
+    } else {

[wkorman, 2017/05/18 00:45:58]

nit: maybe more readable if we add

if (!composited_element_ids.has_value())
  return false;

at start of block and rm else.

       return false;
+    }
   }
 
   return Playing();
 }
 
 bool Animation::IsCandidateForAnimationOnCompositor(
     const Optional<CompositorElementIdSet>& composited_element_ids) const {
   if (!CanStartAnimationOnCompositor(composited_element_ids))
     return false;
 
@@ skipping 431 matching lines @@
   DCHECK(!compositor_player_);
 }
 
 void Animation::CompositorAnimationPlayerHolder::Detach() {
   DCHECK(compositor_player_);
   compositor_player_->SetAnimationDelegate(nullptr);
   animation_ = nullptr;
   compositor_player_.reset();
 }
 }  // namespace blink