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,
+    uint64_t 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<uint64_t>::max() /
+                                              kNumSubElementTypes);
+  uint64_t element_id = dom_node_id;
+  element_id =
+      element_id << 2;  // Shift to make room for sub_element_id enum bits.
+  element_id += static_cast<uint64_t>(sub_element_id);
+  return CompositorElementId(element_id);
+}
+
+uint64_t DomNodeIdFromCompositorElementId(CompositorElementId id) {

[wkorman, 2017/05/05 20:06:10]

Naming style question -- feel like usually we see method names for conversions
like this as XToY rather than YFromX. Which is preferred / more common?

[chrishtr, 2017/05/05 20:46:09]

Not sure. Happy to change if you want.

+  return id >> 2;
+}
+
+CompositorSubElementId SubElementIdFromCompositorElementId(
+    CompositorElementId id) {
+  return static_cast<CompositorSubElementId>(id % kNumSubElementTypes);
 }
 
 }  // namespace blink