[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"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsLayerClient.h"
 #include "platform/graphics/paint/PaintController.h"
+#include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/Vector.h"
-#include <memory>
 
 namespace cc {
 class Layer;
 }
 
 namespace gfx {
 class Vector2dF;
 }
 
 namespace blink {
 
 class GeometryMapper;
 class JSONObject;
 class PaintArtifact;
 class WebLayer;
 struct PaintChunk;
 
+using CompositorElementIdSet = HashSet<CompositorElementId,
+                                       CompositorElementIdHash,
+                                       CompositorElementIdHashTraits>;
+
 // Responsible for managing compositing in terms of a PaintArtifact.
 //
 // Owns a subtree of the compositor layer tree, and updates it in response to
 // changes in the paint artifact.
 //
 // PaintArtifactCompositor is the successor to PaintLayerCompositor, reflecting
 // the new home of compositing decisions after paint in Slimming Paint v2.
 class PLATFORM_EXPORT PaintArtifactCompositor {
   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 |compositedAnimationElementIds| 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,
-      GeometryMapper&);
+      GeometryMapper&,
+      CompositorElementIdSet& compositedAnimationElementIds);
 
   // 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 125 matching lines @@
                            PendingLayer);
   FRIEND_TEST_ALL_PREFIXES(PaintArtifactCompositorTestWithPropertyTrees,
                            PendingLayerWithGeometry);
   FRIEND_TEST_ALL_PREFIXES(PaintArtifactCompositorTestWithPropertyTrees,
                            PendingLayerKnownOpaque);
 };
 
 }  // namespace blink
 
 #endif  // PaintArtifactCompositor_h