Stop retrieving scrolling element id from the CompositorElementId.

third_party/WebKit/Source/platform/graphics/CompositorElementId.cpp

 // 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 "platform/graphics/CompositorElementId.h"
 
 namespace blink {
 
 static CompositorElementId CreateCompositorElementId(
     uint64_t blink_id,
@@ skipping 15 matching lines @@
                                  CompositorElementIdNamespace namespace_id) {
   return CreateCompositorElementId(id, namespace_id);
 }
 
 CompositorElementId PLATFORM_EXPORT
 CompositorElementIdFromScrollbarId(ScrollbarId id,
                                    CompositorElementIdNamespace namespace_id) {
   return CreateCompositorElementId(id, namespace_id);
 }
 
-uint64_t IdFromCompositorElementId(CompositorElementId element_id) {
-  return element_id.id_ >> kCompositorNamespaceBitCount;
-}
-
 CompositorElementIdNamespace NamespaceFromCompositorElementId(
     CompositorElementId element_id) {
   return static_cast<CompositorElementIdNamespace>(
       element_id.id_ %
       static_cast<uint64_t>(
           CompositorElementIdNamespace::kMaxRepresentableNamespaceId));
 }
 
 }  // namespace blink