[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 6e6d1feee9285c2f60240eef3b188a27f21d6a05..fde4c6908842d160730d691dd34444fda4f0700e 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
@@ -5,6 +5,7 @@
 #ifndef PaintArtifactCompositor_h
 #define PaintArtifactCompositor_h
 
+#include <memory>
 #include "base/memory/ref_counted.h"
 #include "platform/PlatformExport.h"
 #include "platform/RuntimeEnabledFeatures.h"
@@ -13,7 +14,6 @@
 #include "wtf/Noncopyable.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/Vector.h"
-#include <memory>
 
 namespace cc {
 class Layer;
@@ -49,6 +49,10 @@ class PLATFORM_EXPORT 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).
@@ -56,7 +60,8 @@ class PLATFORM_EXPORT PaintArtifactCompositor {
       const PaintArtifact&,
       RasterInvalidationTrackingMap<const PaintChunk>* paintChunkInvalidations,
       bool storeDebugInfo,
-      GeometryMapper&);
+      GeometryMapper&,
+      CompositorElementIdSet& compositedElementIds);
 
   // The root layer of the tree managed by this object.
   cc::Layer* rootLayer() const { return m_rootLayer.get(); }