[api] Prototype WeakRef implementation

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 8653ce9b97997701d9dc959339d74018bebd2bc2..892007f853bcf924762e542bbc87bc9ff1a4f738 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -4025,6 +4025,16 @@ void Genesis::InitializeGlobal_harmony_promise_finally() {
   }
 }
 
+void Genesis::InitializeGlobal_harmony_weakref() {
+  if (!FLAG_harmony_weakref) return;
+
+  Handle<JSFunction> js_weak_ref_fun = InstallFunction(
+      global, "WeakRef", JS_WEAK_REF_TYPE, JSWeakRef::kSize,
+      isolate->initial_object_prototype(), Builtins::kIllegal);
+  InstallWithIntrinsicDefaultProto(isolate, js_weak_ref_fun,
+                                   Context::JS_WEAK_REF_FUN_INDEX);
+}
+
 void Genesis::InitializeGlobal_harmony_regexp_dotall() {
   if (!FLAG_harmony_regexp_dotall) return;