Add a copy of webrtc's TaskRunner abstraction, which is going to be deleted in webrtc.

jingle/glue/task_pump.h

 // Copyright (c) 2012 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.
 
 #ifndef JINGLE_GLUE_TASK_PUMP_H_
 #define JINGLE_GLUE_TASK_PUMP_H_
 
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
-#include "third_party/webrtc/base/taskrunner.h"
+#include "third_party/libjingle_xmpp/task_runner/taskrunner.h"
 
 namespace jingle_glue {
 
 // rtc::TaskRunner implementation that works on chromium threads.
 class TaskPump : public rtc::TaskRunner, public base::NonThreadSafe {
  public:
   TaskPump();
 
   ~TaskPump() override;
 
@@ skipping 12 matching lines @@
   bool stopped_;
 
   base::WeakPtrFactory<TaskPump> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskPump);
 };
 
 }  // namespace jingle_glue
 
 #endif  // JINGLE_GLUE_TASK_PUMP_H_