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

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

Index: third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
diff --git a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
index c5464c855b5e983cc2c568fd2fcdc30d9c0d773b..ecac79169d1afc1a860fcdcd8382228568155648 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
@@ -5,15 +5,16 @@
 #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;
@@ -31,6 +32,10 @@ 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
@@ -49,6 +54,10 @@ class PLATFORM_EXPORT 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).
@@ -56,7 +65,8 @@ class PLATFORM_EXPORT PaintArtifactCompositor {
       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(); }