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

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h

 // 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.
 
 #ifndef PaintArtifactCompositor_h
 #define PaintArtifactCompositor_h
 
 #include <memory>
 #include "base/memory/ref_counted.h"
 #include "platform/PlatformExport.h"
@@ skipping 31 matching lines @@
   WTF_MAKE_NONCOPYABLE(PaintArtifactCompositor);
 
  public:
   ~PaintArtifactCompositor();
 
   static std::unique_ptr<PaintArtifactCompositor> create() {
     return WTF::wrapUnique(new PaintArtifactCompositor());
   }
 
   // Updates the layer tree to match the provided paint artifact.
+  //
+  // Populates |compositedElementIds| with the CompositorElementId of all
+  // animations for which we saw a paint chunk and created a layer.
+  //
   // If |storeDebugInfo| is true, stores detailed debugging information in
   // the layers that will be output as part of a call to layersAsJSON
   // (if LayerTreeIncludesDebugInfo is specified).
   void update(
       const PaintArtifact&,
       RasterInvalidationTrackingMap<const PaintChunk>* paintChunkInvalidations,
-      bool storeDebugInfo);
+      bool storeDebugInfo,
+      CompositorElementIdSet& compositedElementIds);
 
   // The root layer of the tree managed by this object.
   cc::Layer* rootLayer() const { return m_rootLayer.get(); }
 
   // Wraps rootLayer(), so that it can be attached as a child of another
   // WebLayer.
   WebLayer* getWebLayer() const { return m_webLayer.get(); }
 
   // Returns extra information recorded during unit tests.
   // While not part of the normal output of this class, this provides a simple
@@ skipping 143 matching lines @@
                            PendingLayer);
   FRIEND_TEST_ALL_PREFIXES(PaintArtifactCompositorTestWithPropertyTrees,
                            PendingLayerWithGeometry);
   FRIEND_TEST_ALL_PREFIXES(PaintArtifactCompositorTestWithPropertyTrees,
                            PendingLayerKnownOpaque_DISABLED);
 };
 
 }  // namespace blink
 
 #endif  // PaintArtifactCompositor_h