Decouple root visitors from object visitors.

src/v8threads.cc

Index: src/v8threads.cc
diff --git a/src/v8threads.cc b/src/v8threads.cc
index 34d26ece7f12d087c640b46b85f47e4909c52941..c0470c5b3c4fcf12d735e19d098034a1ab496feb 100644
--- a/src/v8threads.cc
+++ b/src/v8threads.cc
@@ -10,6 +10,7 @@
 #include "src/execution.h"
 #include "src/isolate-inl.h"
 #include "src/regexp/regexp-stack.h"
+#include "src/visitors.h"
 
 namespace v8 {
 
@@ -288,7 +289,7 @@ void ThreadManager::EagerlyArchiveThread() {
   state->LinkInto(ThreadState::IN_USE_LIST);
   char* to = state->data();
   // Ensure that data containing GC roots are archived first, and handle them
-  // in ThreadManager::Iterate(ObjectVisitor*).
+  // in ThreadManager::Iterate(RootVisitor*).
   to = isolate_->handle_scope_implementer()->ArchiveThread(to);
   to = isolate_->ArchiveThread(to);
   to = Relocatable::ArchiveState(isolate_, to);
@@ -320,8 +321,7 @@ bool ThreadManager::IsArchived() {
   return data != NULL && data->thread_state() != NULL;
 }
 
-
-void ThreadManager::Iterate(ObjectVisitor* v) {
+void ThreadManager::Iterate(RootVisitor* v) {
   // Expecting no threads during serialization/deserialization
   for (ThreadState* state = FirstThreadStateInUse();
        state != NULL;