Decouple root visitors from object visitors.

src/v8threads.h

Index: src/v8threads.h
diff --git a/src/v8threads.h b/src/v8threads.h
index db0ed070fae1f3ee6265e26ffa53479c79690751..8fc6f0c62f6ad69c498d8d2e9a059e5a80d7c25a 100644
--- a/src/v8threads.h
+++ b/src/v8threads.h
@@ -10,6 +10,8 @@
 namespace v8 {
 namespace internal {
 
+class RootVisitor;
+class ThreadLocalTop;
 
 class ThreadState {
  public:
@@ -51,11 +53,6 @@ class ThreadState {
   friend class ThreadManager;
 };
 
-
-// Defined in isolate.h.
-class ThreadLocalTop;
-
-
 class ThreadVisitor {
  public:
   // ThreadLocalTop may be only available during this call.
@@ -65,7 +62,6 @@ class ThreadVisitor {
   virtual ~ThreadVisitor() {}
 };
 
-
 class ThreadManager {
  public:
   void Lock();
@@ -76,7 +72,7 @@ class ThreadManager {
   void FreeThreadResources();
   bool IsArchived();
 
-  void Iterate(ObjectVisitor* v);
+  void Iterate(RootVisitor* v);
   void IterateArchivedThreads(ThreadVisitor* v);
   bool IsLockedByCurrentThread() {
     return mutex_owner_.Equals(ThreadId::Current());