Store compositor element id in paint properties for animated objects.

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilderTest.h

 // Copyright 2016 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.
 
 #include "core/layout/LayoutTestHelper.h"
 #include "platform/testing/RuntimeEnabledFeaturesTestHelpers.h"
 #include "platform/testing/UnitTestHelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
@@ skipping 22 matching lines @@
   // FrameView, accounting for differences from the RootLayerScrolls setting.
   const TransformPaintPropertyNode* framePreTranslation();
   const TransformPaintPropertyNode* frameScrollTranslation();
   const ClipPaintPropertyNode* frameContentClip();
   const ScrollPaintPropertyNode* frameScroll(FrameView* = nullptr);
 
   // Return the local border box's paint offset. For more details, see
   // ObjectPaintProperties::localBorderBoxProperties().
   LayoutPoint paintOffset(const LayoutObject*);
 
+  const ObjectPaintProperties* paintPropertiesForElement(const char* name);
+
  private:
   void SetUp() override;
   void TearDown() override;
 };
 
 }  // namespace blink