WTF: Support enums in DefaultHash and HashTraits by casting to integral types.

third_party/WebKit/Source/wtf/HashTraits.h

Index: third_party/WebKit/Source/wtf/HashTraits.h
diff --git a/third_party/WebKit/Source/wtf/HashTraits.h b/third_party/WebKit/Source/wtf/HashTraits.h
index 6c9580a413bfe1a2da552a9b0761ed97a811b255..c4319ce235c80284cfa1fb738401502c2bb5faef 100644
--- a/third_party/WebKit/Source/wtf/HashTraits.h
+++ b/third_party/WebKit/Source/wtf/HashTraits.h
@@ -35,7 +35,7 @@
 
 namespace WTF {
 
-template <bool isInteger, typename T>
+template <bool isInteger, bool isEnum, typename T>
 struct GenericHashTraitsBase;
 template <typename T>
 struct HashTraits;
@@ -46,7 +46,7 @@ enum ShouldWeakPointersBeMarkedStrongly {
 };
 
 template <typename T>
-struct GenericHashTraitsBase<false, T> {
+struct GenericHashTraitsBase<false, false, T> {
   // The emptyValueIsZero flag is used to optimize allocation of empty hash
   // tables with zeroed memory.
   static const bool emptyValueIsZero = false;
@@ -88,12 +88,16 @@ struct GenericHashTraitsBase<false, T> {
   static const WeakHandlingFlag weakHandlingFlag =
       IsWeak<T>::value ? WeakHandlingInCollections
                        : NoWeakHandlingInCollections;
+
+  static T emptyValue() { return T(); }
 };
 
 // Default integer traits disallow both 0 and -1 as keys (max value instead of
 // -1 for unsigned).
 template <typename T>
-struct GenericHashTraitsBase<true, T> : GenericHashTraitsBase<false, T> {
+struct GenericHashTraitsBase<true, false, T>
+    : GenericHashTraitsBase<false, false, T> {
+  static_assert(std::is_integral<T>::value, "These traits are for integers");
   static const bool emptyValueIsZero = true;
   static void constructDeletedValue(T& slot, bool) {
     slot = static_cast<T>(-1);
@@ -101,14 +105,26 @@ struct GenericHashTraitsBase<true, T> : GenericHashTraitsBase<false, T> {
   static bool isDeletedValue(T value) { return value == static_cast<T>(-1); }
 };
 
+// Default enum traits disallow both -1 and -2 as keys (max and max-1 for
+// enums with unsigned underlying types).
 template <typename T>
-struct GenericHashTraits
-    : GenericHashTraitsBase<std::is_integral<T>::value, T> {
+struct GenericHashTraitsBase<false, true, T>
+    : GenericHashTraitsBase<false, false, T> {
+  static_assert(std::is_enum<T>::value, "These traits are for enums");
+  static T emptyValue() { return static_cast<T>(-1); }
+  static void constructDeletedValue(T& slot, bool) {
+    slot = static_cast<T>(-2);
+  }
+  static bool isDeletedValue(T value) { return value == static_cast<T>(-2); }
+};
+
+template <typename T>
+struct GenericHashTraits : GenericHashTraitsBase<std::is_integral<T>::value,
+                                                 std::is_enum<T>::value,
+                                                 T> {
   typedef T TraitType;
   typedef T EmptyValueType;
 
-  static T emptyValue() { return T(); }
-
   // Type for functions that do not take ownership, such as contains.
   typedef const T& PeekInType;
   typedef T* IteratorGetType;