Change cc::ElementId to be a uint64_t

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

Index: third_party/WebKit/Source/platform/graphics/CompositorElementId.h
diff --git a/third_party/WebKit/Source/platform/graphics/CompositorElementId.h b/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
index 7a17e46a932681b5b9bdd6454c6d20fa3ae7f409..410b0a3aaa430ffcfc45dc8041d6db66bda9e949 100644
--- a/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
+++ b/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
@@ -13,46 +13,27 @@
 
 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);
-
-// 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;
-};
+    CreateCompositorElementId(DOMNodeId, CompositorSubElementId);
 
-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);
-  }
-};
+DOMNodeId PLATFORM_EXPORT DomNodeIdFromCompositorElementId(CompositorElementId);
+CompositorSubElementId PLATFORM_EXPORT
+    SubElementIdFromCompositorElementId(CompositorElementId);
 
-using CompositorElementIdSet = HashSet<CompositorElementId,
-                                       CompositorElementIdHash,
-                                       CompositorElementIdHashTraits>;
+using CompositorElementIdSet = HashSet<CompositorElementId::Id>;
 
 }  // namespace blink