blink: Cleanup class/struct forward declarations

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 061ae6a809d268ae3aa1fc0b76c378e154c2a8e4..6c9580a413bfe1a2da552a9b0761ed97a811b255 100644
--- a/third_party/WebKit/Source/wtf/HashTraits.h
+++ b/third_party/WebKit/Source/wtf/HashTraits.h
@@ -419,19 +419,6 @@ struct NullableHashTraits : public HashTraits<T> {
   static T emptyValue() { return reinterpret_cast<T>(1); }
 };
 
-// This is for tracing inside collections that have special support for weak
-// pointers. The trait has a trace method which returns true if there are weak
-// pointers to things that have not (yet) been marked live. Returning true
-// indicates that the entry in the collection may yet be removed by weak
-// handling. Default implementation for non-weak types is to use the regular
-// non-weak TraceTrait. Default implementation for types with weakness is to
-// call traceInCollection on the type's trait.
-template <WeakHandlingFlag weakHandlingFlag,
-          ShouldWeakPointersBeMarkedStrongly strongify,
-          typename T,
-          typename Traits>
-struct TraceInCollectionTrait;
-
 }  // namespace WTF
 
 using WTF::HashTraits;