Add WeakMap to v8.h

src/runtime/runtime.h

Index: src/runtime/runtime.h
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index dca28f1ad44cba3d36fa5deae24263cf2af22b9d..33852150d78b1b5d421e16be2c4791ff5522d41c 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -879,6 +879,13 @@ class Runtime : public AllStatic {
   MUST_USE_RESULT static MaybeHandle<Object> CreateArrayLiteralBoilerplate(
       Isolate* isolate, Handle<FixedArray> literals,
       Handle<FixedArray> elements);
+
+  static void WeakCollectionInitialize(
+      Isolate* isolate, Handle<JSWeakCollection> weak_collection);
+  static void WeakCollectionSet(Handle<JSWeakCollection> weak_collection,
+                                Handle<Object> key, Handle<Object> value);
+  static bool WeakCollectionDelete(Handle<JSWeakCollection> weak_collection,
+                                   Handle<Object> key);
 };