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

Source/platform/heap/Visitor.h

Index: Source/platform/heap/Visitor.h
diff --git a/Source/platform/heap/Visitor.h b/Source/platform/heap/Visitor.h
index 7ca67f89b5b3cf5499440d9c488c10044faab9ce..36b8123bfb9d408f8e4618a16cbef28e96844083 100644
--- a/Source/platform/heap/Visitor.h
+++ b/Source/platform/heap/Visitor.h
@@ -194,13 +194,14 @@ class TraceTrait {
 public:
     // Default implementation of TraceTrait<T>::trace just statically
     // dispatches to the trace method of the class T.
-    template<typename TraceDispatcher>
-    static void trace(TraceDispatcher visitor, void* self)
+    template<typename VisitorDispatcher>
+    static void trace(VisitorDispatcher visitor, void* self)
     {
         TraceCompatibilityAdaptor<T>::trace(visitor, static_cast<T*>(self));
     }
 
-    static void mark(Visitor* visitor, const T* t)
+    template<typename VisitorDispatcher>
+    static void mark(VisitorDispatcher visitor, const T* t)
     {
         DefaultTraceTrait<T>::mark(visitor, t);
     }
@@ -653,7 +654,8 @@ template<typename T, size_t N>
 struct OffHeapCollectionTraceTrait<WTF::Vector<T, N, WTF::DefaultAllocator> > {
     typedef WTF::Vector<T, N, WTF::DefaultAllocator> Vector;
 
-    static void trace(Visitor* visitor, const Vector& vector)
+    template<typename VisitorDispatcher>
+    static void trace(VisitorDispatcher visitor, const Vector& vector)
     {
         if (vector.isEmpty())
             return;
@@ -666,7 +668,8 @@ template<typename T, size_t N>
 struct OffHeapCollectionTraceTrait<WTF::Deque<T, N> > {
     typedef WTF::Deque<T, N> Deque;
 
-    static void trace(Visitor* visitor, const Deque& deque)
+    template<typename VisitorDispatcher>
+    static void trace(VisitorDispatcher visitor, const Deque& deque)
     {
         if (deque.isEmpty())
             return;
@@ -687,7 +690,8 @@ public:
 template<typename T>
 class DefaultTraceTrait<T, false> {
 public:
-    static void mark(Visitor* visitor, const T* t)
+    template<typename VisitorDispatcher>
+    static void mark(VisitorDispatcher visitor, const T* t)
     {
         // Default mark method of the trait just calls the two-argument mark
         // method on the visitor. The second argument is the static trace method
@@ -727,7 +731,8 @@ public:
 template<typename T>
 class DefaultTraceTrait<T, true> {
 public:
-    static void mark(Visitor* visitor, const T* self)
+    template<typename VisitorDispatcher>
+    static void mark(VisitorDispatcher visitor, const T* self)
     {
         if (!self)
             return;