Change cc::ElementId to be a uint64_t

third_party/WebKit/Source/platform/graphics/CompositorElementId.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.
 
 #ifndef CompositorElementId_h
 #define CompositorElementId_h
 
 #include "cc/trees/element_id.h"
 #include "platform/PlatformExport.h"
 #include "platform/wtf/HashFunctions.h"
 #include "platform/wtf/HashSet.h"
 #include "platform/wtf/HashTraits.h"
 
 namespace blink {
 
-enum class CompositorSubElementId {
-  kPrimary,
-  kScroll,
-  kViewport,
-  kLinkHighlight
+// Do not add more of these without adjusting the bitfield arithmetic in
+// CreateCompositorElementId.
+enum CompositorSubElementId {
+  kPrimary = 0,
+  kScroll = 1,
+  kViewport = 2,
+  kLinkHighlight = 3,
+  kNumSubElementTypes = 4

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

Add a blank line and comment before this entry to make it obvious that it is a
different kind of thing, and that any new values for the enum should be added
before it. To avoid mistakes in the value for kNumSubElementTypes, you might
want to use the auto-one-more-than-last-entry value instead of specifying the
value.

Random thought: Is there any chance that by including this value in the enum,
the compiler decides it needs more bits to store a CompositorSubElementId, in
such a way that results in a performance/size regression?

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

Done.
I don't think so, because it isn't actually stored anywhere other than
in method parameters after this CL.

 };
 
 using CompositorElementId = cc::ElementId;
+using DOMNodeId = uint64_t;
 
 CompositorElementId PLATFORM_EXPORT
-CreateCompositorElementId(int dom_node_id, CompositorSubElementId);
+    CreateCompositorElementId(DOMNodeId, CompositorSubElementId);
 
-// Note cc::ElementId has a hash function already implemented via
-// ElementIdHash::operator(). However for consistency's sake we choose to use
-// Blink's hash functions with Blink specific data structures.
-struct CompositorElementIdHash {
-  static unsigned GetHash(const CompositorElementId& p) {
-    return WTF::HashInts(p.primaryId, p.secondaryId);
-  }
-  static bool Equal(const CompositorElementId& a,
-                    const CompositorElementId& b) {
-    return a.primaryId == b.primaryId && a.secondaryId == b.secondaryId;
-  }
-  static const bool safe_to_compare_to_empty_or_deleted = true;
-};
+DOMNodeId PLATFORM_EXPORT DomNodeIdFromCompositorElementId(CompositorElementId);
+CompositorSubElementId PLATFORM_EXPORT
+    SubElementIdFromCompositorElementId(CompositorElementId);
 
-struct CompositorElementIdHashTraits
-    : WTF::GenericHashTraits<CompositorElementId> {
-  static CompositorElementId EmptyValue() { return CompositorElementId(); }
-  static void ConstructDeletedValue(CompositorElementId& slot, bool) {
-    slot = CompositorElementId(-1, -1);
-  }
-  static bool IsDeletedValue(CompositorElementId value) {
-    return value == CompositorElementId(-1, -1);
-  }
-};
-
-using CompositorElementIdSet = HashSet<CompositorElementId,
-                                       CompositorElementIdHash,
-                                       CompositorElementIdHashTraits>;
+using CompositorElementIdSet = HashSet<CompositorElementId::Id>;
 
 }  // namespace blink
 
 #endif  // CompositorElementId_h