Change cc::ElementId to be a uint64_t

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 {
 
 CompositorElementId CreateCompositorElementId(
-    int dom_node_id,
+    DOMNodeId dom_node_id,
     CompositorSubElementId sub_element_id) {
-  return CompositorElementId(dom_node_id, static_cast<int>(sub_element_id));
+  DCHECK(dom_node_id > 0 &&
+         dom_node_id <
+             std::numeric_limits<DOMNodeId>::max() / kNumSubElementTypes);
+  CompositorElementId element_id;
+  element_id.id = dom_node_id;
+  element_id.id = element_id.id

[suzyh_UTC10 (ex-contributor), 2017/05/08 01:04:15]

Could you just write
element_id.id = dom_node_id << 2;  // Shift to ....
here instead?

[chrishtr, 2017/05/08 16:32:13]

Done.

+                  << 2;  // Shift to make room for sub_element_id enum bits.
+  element_id.id += static_cast<uint64_t>(sub_element_id);
+  return element_id;
+}
+
+DOMNodeId DomNodeIdFromCompositorElementId(CompositorElementId element_id) {
+  return element_id.id >> 2;
+}
+
+CompositorSubElementId SubElementIdFromCompositorElementId(

[suzyh_UTC10 (ex-contributor), 2017/05/08 01:04:15]

Do these functions belong inside the definition of ElementId instead of as
separate helper functions?

[chrishtr, 2017/05/08 16:32:13]

No, because that type is defined in cc and by design cc doesn't know about
the needs of "clients" like Blink or ui/

+    CompositorElementId element_id) {
+  return static_cast<CompositorSubElementId>(element_id.id %
+                                             kNumSubElementTypes);
 }
 
 }  // namespace blink