Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h b/third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h
index 2f095e49575a5243d506470509a6bdc295a2ad9d..e4605135e9616e5a99a6eacb3167bceea6d52377 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h
@@ -27,7 +27,7 @@ namespace blink {
 struct PaintChunkProperties {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
-  PaintChunkProperties() : backfaceHidden(false) {}
+  PaintChunkProperties() : backfaceHidden(false), willChangeTransform(false) {}
 
   // TODO(pdr): Refactor these to use PropertyTreeState.
   RefPtr<const TransformPaintPropertyNode> transform;
@@ -35,6 +35,11 @@ struct PaintChunkProperties {
   RefPtr<const EffectPaintPropertyNode> effect;
   RefPtr<const ScrollPaintPropertyNode> scroll;
   bool backfaceHidden;
+  bool willChangeTransform;
+
+  bool hasDirectCompositingReasons() const {
+    return backfaceHidden || willChangeTransform;
+  }
 };
 
 // Equality is based only on the pointers and is not 'deep' which would require
@@ -44,7 +49,8 @@ inline bool operator==(const PaintChunkProperties& a,
   return a.transform.get() == b.transform.get() &&
          a.clip.get() == b.clip.get() && a.effect.get() == b.effect.get() &&
          a.scroll.get() == b.scroll.get() &&
-         a.backfaceHidden == b.backfaceHidden;
+         a.backfaceHidden == b.backfaceHidden &&
+         a.willChangeTransform == b.willChangeTransform;
 }
 
 inline bool operator!=(const PaintChunkProperties& a,