[SPv2] Decomposite otherwise-compositable animations that paint nothing.

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

 // 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 "core/paint/PaintPropertyTreeBuilder.h"
 
 #include <memory>
 #include "core/dom/DOMNodeIds.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 55 matching lines @@
                                 std::move(localTransformSpace), clipRect);
     return false;
   }
   frameView.setContentClip(ClipPaintPropertyNode::create(
       std::move(parent), std::move(localTransformSpace), clipRect));
   return true;
 }
 
 static CompositorElementId createDomNodeBasedCompositorElementId(
     const LayoutObject& object) {
+  // TODO(wkorman): Centralize this implementation with similar across
+  // animation, scrolling and compositing logic.
   return createCompositorElementId(DOMNodeIds::idForNode(object.node()),
                                    CompositorSubElementId::Primary);
 }
 
 // True if a new property was created or a main thread scrolling reason changed
 // (which can affect descendants), false if an existing one was updated.
 static bool updateScrollTranslation(
     FrameView& frameView,
     PassRefPtr<const TransformPaintPropertyNode> parent,
     const TransformationMatrix& matrix,
@@ skipping 1038 matching lines @@
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 
   context.forceSubtreeUpdate |= object.subtreeNeedsPaintPropertyUpdate();
 }
 
 }  // namespace blink