Use v8::MicrotasksScope internally in V8RecursionScope.

gin/run_microtasks_observer.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gin/run_microtasks_observer.h"
 
 namespace gin {
 
 RunMicrotasksObserver::RunMicrotasksObserver(v8::Isolate* isolate)
     : isolate_(isolate) {
 }
 
 void RunMicrotasksObserver::WillProcessTask(const base::PendingTask& task) {
 }
 
 void RunMicrotasksObserver::DidProcessTask(const base::PendingTask& task) {
   v8::Isolate::Scope scope(isolate_);
-  isolate_->RunMicrotasks();
+  v8::MicrotasksScope::PerformCheckpoint(isolate_);
 }
 
 }  // namespace gin