TaskClosureAdapter::Run does not invoke the task if it is null.

base/task.cc

 // Copyright (c) 2011 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 "base/task.h"
 
 Task::Task() {
 }
 
 Task::~Task() {
@@ skipping 35 matching lines @@
       should_leak_task_(should_leak_task) {
 }
 
 TaskClosureAdapter::~TaskClosureAdapter() {
   if (!*should_leak_task_) {
     delete task_;
   }
 }
 
 void TaskClosureAdapter::Run() {
-  task_->Run();
-  delete task_;
-  task_ = NULL;
+  if (task_) {
+    task_->Run();
+    delete task_;
+    task_ = NULL;
+  }
 }
 
 // Don't leak tasks by default.
 bool TaskClosureAdapter::kTaskLeakingDefault = false;
 
 }  // namespace subtle
 
 }  // namespace base