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

Source/platform/heap/HeapTest.cpp

Index: Source/platform/heap/HeapTest.cpp
diff --git a/Source/platform/heap/HeapTest.cpp b/Source/platform/heap/HeapTest.cpp
index 082238d432c4166f889ac9a4847d943a7c2ee755..adac6c1dad3c5eee4b1a039b7fbe1db529510cac 100644
--- a/Source/platform/heap/HeapTest.cpp
+++ b/Source/platform/heap/HeapTest.cpp
@@ -58,7 +58,7 @@ public:
     }
 
     static int s_destructorCalls;
-    static void trace(Visitor*) { }
+    void trace(Visitor*) { }
 
     int value() const { return m_x; }
 
@@ -72,6 +72,7 @@ private:
     IntWrapper();
     int m_x;
 };
+static_assert(WTF::NeedsTracing<IntWrapper>::value, "NeedsTracing macro failed to recognize trace method.");
 
 class ThreadMarker {
 public:
@@ -3642,6 +3643,8 @@ TEST(HeapTest, CollectionNesting)
     typedef HeapDeque<Member<IntWrapper> > IntDeque;
     HeapHashMap<void*, IntVector>* map = new HeapHashMap<void*, IntVector>();
     HeapHashMap<void*, IntDeque>* map2 = new HeapHashMap<void*, IntDeque>();
+    static_assert(WTF::NeedsTracing<IntVector>::value, "Failed to recognize HeapVector as NeedsTracing");
+    static_assert(WTF::NeedsTracing<IntDeque>::value, "Failed to recognize HeapDeque as NeedsTracing");
 
     map->add(key, IntVector());
     map2->add(key, IntDeque());