[compositor-worker] Create property tree nodes for proxies.

cc/animation/mutable_properties.h

Index: cc/animation/mutable_properties.h
diff --git a/cc/animation/mutable_properties.h b/cc/animation/mutable_properties.h
index daec22566b9808a6e7f63e5a80d9da73be61cd27..1938313a757ee152e2a9a25123e6cf3dddedba08 100644
--- a/cc/animation/mutable_properties.h
+++ b/cc/animation/mutable_properties.h
@@ -15,6 +15,7 @@ struct MutableProperty {
   enum : uint32_t { kScrollLeft = 1 << 1 };
   enum : uint32_t { kScrollTop = 1 << 2 };
   enum : uint32_t { kTransform = 1 << 3 };
+  enum : uint32_t { kTransformRelated = kTransform | kScrollLeft | kScrollTop };
 
   enum : int { kNumProperties = 4 };
 };