Fix data-race in default implementation of delayed task.

src/libplatform/default-platform.cc

 // Copyright 2013 the V8 project 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 "src/libplatform/default-platform.h"
 
 #include <algorithm>
 #include <queue>
 
 #include "src/base/logging.h"
@@ skipping 131 matching lines @@
 
 void DefaultPlatform::CallOnForegroundThread(v8::Isolate* isolate, Task* task) {
   base::LockGuard<base::Mutex> guard(&lock_);
   main_thread_queue_[isolate].push(task);
 }
 
 
 void DefaultPlatform::CallDelayedOnForegroundThread(Isolate* isolate,
                                                     Task* task,
                                                     double delay_in_seconds) {
+  base::LockGuard<base::Mutex> guard(&lock_);
   double deadline = MonotonicallyIncreasingTime() + delay_in_seconds;
   main_thread_delayed_queue_[isolate].push(std::make_pair(deadline, task));
 }
 
 
 double DefaultPlatform::MonotonicallyIncreasingTime() {
   return base::TimeTicks::HighResolutionNow().ToInternalValue() /
          static_cast<double>(base::Time::kMicrosecondsPerSecond);
 }
 } }  // namespace v8::platform