Rename and improve "traceable" templates.

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 77d4ff6bc35987f584449ad72aed5c9bfcd1347a..bd8f8c9d7bc9e8c40d21d46fb4b5017a4737b31c 100644
--- a/third_party/WebKit/Source/wtf/HashTraits.h
+++ b/third_party/WebKit/Source/wtf/HashTraits.h
@@ -61,9 +61,13 @@ template <typename T> struct GenericHashTraitsBase<false, T> {
     static const unsigned minimumTableSize = 8;
 #endif
 
+    // When a hash table backing store is traced, its elements will be
+    // traced if their class type has a trace method. However, weak-referenced
+    // elements should not be traced then, but handled by the weak processing
+    // phase that follows.
     template <typename U = void>
-    struct NeedsTracingLazily {

[haraken, 2016/06/12 07:11:31]

Nit: I'm okay with keeping the word "lazily" to make it clearer that the trait
needs to be instantiated lazily.

BTW, do we have any verification that the trait is instantiated lazily (i.e., at
a proper timing)?

[sof, 2016/06/12 07:29:44]

None other than it would fail to compile, i think. Exposing that (instantiation)
implementation detail in the name of this nested template, doesn't gain us much
imho.

-        static const bool value = NeedsTracing<T>::value;
+    struct IsTraceableInCollection {
+        static const bool value = IsTraceable<T>::value && !IsWeak<T>::value;
     };
 
     // The NeedsToForbidGCOnMove flag is used to make the hash table move
@@ -302,8 +306,8 @@ struct KeyValuePairHashTraits : GenericHashTraits<KeyValuePair<typename KeyTrait
     static EmptyValueType emptyValue() { return KeyValuePair<typename KeyTraits::EmptyValueType, typename ValueTraits::EmptyValueType>(KeyTraits::emptyValue(), ValueTraits::emptyValue()); }
 
     template <typename U = void>
-    struct NeedsTracingLazily {
-        static const bool value = NeedsTracingTrait<KeyTraits>::value || NeedsTracingTrait<ValueTraits>::value;
+    struct IsTraceableInCollection {
+        static const bool value = IsTraceableInCollectionTrait<KeyTraits>::value || IsTraceableInCollectionTrait<ValueTraits>::value;
     };
 
     template <typename U = void>