Add WeakMap to v8.h

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 8226a0e5d7f0e92dfe4775a327fee2776b16a55e..c1c818cfeea189c568090e690adf743033bfa355 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -2236,6 +2236,15 @@ Handle<JSObject> Factory::NewArgumentsObject(Handle<JSFunction> callee,
 }
 
 
+Handle<JSWeakMap> Factory::NewJSWeakMap() {
+  // TODO(adamk): Currently the map is only created three times per
+  // isolate. If it's created more often, the map should be moved into the
+  // strong root list.
+  Handle<Map> map = NewMap(JS_WEAK_MAP_TYPE, JSWeakMap::kSize);
+  return Handle<JSWeakMap>::cast(NewJSObjectFromMap(map));
+}
+
+
 Handle<JSFunction> Factory::CreateApiFunction(
     Handle<FunctionTemplateInfo> obj,
     Handle<Object> prototype,