Verify a bit more about external strings

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 37eb00485f7ae463aadeb41b3a5d3a6b4143a70b..95a8f59200890a8d3b03707f346ddc4172ce8d27 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -526,6 +526,31 @@ void Heap::RepairFreeListsAfterDeserialization() {
 }
 
 
+void Heap::FinalizeExternalString(String* string) {
+  DCHECK(string->IsExternalString());
+  v8::String::ExternalStringResourceBase** resource_addr =
+      reinterpret_cast<v8::String::ExternalStringResourceBase**>(
+          reinterpret_cast<byte*>(string) + ExternalString::kResourceOffset -
+          kHeapObjectTag);
+
+  // Dispose of the C++ object if it has not already been disposed.
+  if (*resource_addr != NULL) {
+#ifdef V8_ENABLE_CHECKS
+    {
+      HandleScope scope(string->GetIsolate());
+      i::Handle<i::String> str_obj(string);
+      v8::Utils::ToLocal(str_obj)->VerifyExternalStringResourceBase(
+          *resource_addr, StringShape(string).IsExternalOneByte()
+                              ? v8::String::ONE_BYTE_ENCODING
+                              : v8::String::TWO_BYTE_ENCODING);
+    }
+#endif
+    (*resource_addr)->Dispose();
+    *resource_addr = NULL;
+  }
+}
+
+
 void Heap::ProcessPretenuringFeedback() {
   if (FLAG_allocation_site_pretenuring) {
     int tenure_decisions = 0;