Reland: Templatize visitor arguments for TraceTrait mark and trace methods.

Source/wtf/TypeTraits.h

Index: Source/wtf/TypeTraits.h
diff --git a/Source/wtf/TypeTraits.h b/Source/wtf/TypeTraits.h
index 367978f216561b0aef482a68d4fbc89a0107c3b6..d9eeecdcc448bde2de262491b2c91ca6d28003b5 100644
--- a/Source/wtf/TypeTraits.h
+++ b/Source/wtf/TypeTraits.h
@@ -303,6 +303,7 @@ namespace WTF {
 namespace blink {
 
 class JSONValue;
+class Visitor;
 
 } // namespace blink
 
@@ -317,24 +318,46 @@ namespace WTF {
         };
     };
 
+#if COMPILER(MSVC)
+template<typename T, bool = __is_class(T)> struct NeedsTracingMSVC;
+
+template<typename T>
+struct NeedsTracingMSVC<T, true> {
+    __if_exists(T::trace)
+    {
+        static const bool value = true;
+    }
+    __if_not_exists(T::trace)
+    {
+        static const bool value = false;
+    }
+};
+
+template<typename T>
+struct NeedsTracingMSVC<T, false> {
+    static const bool value = false;
+};
+#endif
+
 template<typename T>
 class NeedsTracing {
+#if COMPILER(MSVC)
+public:
+    static const bool value = NeedsTracingMSVC<T>::value;
+#else
     typedef char YesType;
     typedef struct NoType {
         char padding[8];
     } NoType;
-#if COMPILER(MSVC)
-    template<typename V> static YesType checkHasTraceMethod(char[&V::trace != 0]);
-#else
     template<size_t> struct HasMethod;
-    template<typename V> static YesType checkHasTraceMethod(HasMethod<sizeof(&V::trace)>*);
-#endif // COMPILER(MSVC)
+    template<typename V> static YesType checkHasTraceMethod(HasMethod<sizeof(static_cast<void (V::*)(blink::Visitor*)>(&V::trace))>*);
     template<typename V> static NoType checkHasTraceMethod(...);
 public:
     // We add sizeof(T) to both sides here, because we want it to fail for
     // incomplete types. Otherwise it just assumes that incomplete types do not
     // have a trace method, which may not be true.
-    static const bool value = sizeof(YesType) + sizeof(T) == sizeof(checkHasTraceMethod<T>(0)) + sizeof(T);
+    static const bool value = sizeof(YesType) + sizeof(T) == sizeof(checkHasTraceMethod<T>(nullptr)) + sizeof(T);
+#endif // COMPILER(MSVC)
 };
 
 // Convenience template wrapping the NeedsTracingLazily template in