Decouple root visitors from object visitors.

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index 4243d9025952e9e1366824763d0a23792fe02015..00bda0941ca8f1647d807745969c3725659fc678 100644
--- a/src/api.h
+++ b/src/api.h
@@ -365,7 +365,7 @@ class V8_EXPORT_PRIVATE DeferredHandles {
     isolate->LinkDeferredHandles(this);
   }
 
-  void Iterate(ObjectVisitor* v);
+  void Iterate(RootVisitor* v);
 
   List<Object**> blocks_;
   DeferredHandles* next_;
@@ -417,9 +417,8 @@ class HandleScopeImplementer {
   void FreeThreadResources();
 
   // Garbage collection support.
-  void Iterate(v8::internal::ObjectVisitor* v);
-  static char* Iterate(v8::internal::ObjectVisitor* v, char* data);
-
+  void Iterate(v8::internal::RootVisitor* v);
+  static char* Iterate(v8::internal::RootVisitor* v, char* data);
 
   inline internal::Object** GetSpareOrNewBlock();
   inline void DeleteExtensions(internal::Object** prev_limit);
@@ -534,7 +533,7 @@ class HandleScopeImplementer {
   // This is only used for threading support.
   HandleScopeData handle_scope_data_;
 
-  void IterateThis(ObjectVisitor* v);
+  void IterateThis(RootVisitor* v);
   char* RestoreThreadHelper(char* from);
   char* ArchiveThreadHelper(char* to);