External string table.

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index 1a0c982936f7b45e2fd305a1cee75b8e09171c82..e4bb925f0e9299ea105df757004d0912dad893b0 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -168,6 +168,12 @@ class GlobalHandles::Node : public Malloced {
       if (first_deallocated()) {
         first_deallocated()->set_next(head());
       }
+      // Check that we are not passing a finalized external string to
+      // the callback.
+      ASSERT(!object_->IsExternalAsciiString() ||
+             ExternalAsciiString::cast(object_)->resource() != NULL);
+      ASSERT(!object_->IsExternalTwoByteString() ||
+             ExternalTwoByteString::cast(object_)->resource() != NULL);
       // Leaving V8.
       VMState state(EXTERNAL);
       func(object, par);
@@ -507,5 +513,4 @@ void GlobalHandles::RemoveObjectGroups() {
   object_groups->Clear();
 }
 
-
 } }  // namespace v8::internal