Decouple root visitors from object visitors.

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index 80f32427c65beed55db96924780dac2552c61b6b..3b97e04fb288ab33462784b0ab393d7b61ef42c0 100644
--- a/src/api.h
+++ b/src/api.h
@@ -369,7 +369,7 @@ class V8_EXPORT_PRIVATE DeferredHandles {
     isolate->LinkDeferredHandles(this);
   }
 
-  void Iterate(ObjectVisitor* v);
+  void Iterate(RootVisitor* v);
 
   List<Object**> blocks_;
   DeferredHandles* next_;
@@ -421,9 +421,8 @@ 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);
@@ -538,7 +537,7 @@ 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);