[chrome.displaySource] Add client thread checks to encoders.

extensions/renderer/api/display_source/wifi_display/wifi_display_media_encoder.h

 // Copyright 2016 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 EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_MEDIA_ENCODER_H_
 #define EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_MEDIA_ENCODER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/move.h"
 #include "base/single_thread_task_runner.h"
+#include "base/threading/thread_checker.h"
 
 namespace extensions {
 
 // This structure represents an encoded media unit such as a video frame or
 // a number of audio frames.
 struct WiFiDisplayEncodedUnit {
   WiFiDisplayEncodedUnit(std::string data,
                          base::TimeTicks reference_timestamp,
                          bool key_frame);
   WiFiDisplayEncodedUnit(std::string data,
@@ skipping 29 matching lines @@
   // |error_callback| is invoked to report a fatal encoder error
   void SetCallbacks(const EncodedUnitCallback& encoded_callback,
                     const base::Closure& error_callback);
 
  protected:
   friend class base::RefCountedThreadSafe<WiFiDisplayMediaEncoder>;
 
   WiFiDisplayMediaEncoder();
   virtual ~WiFiDisplayMediaEncoder();
 
+  base::ThreadChecker client_thread_checker_;
   EncodedUnitCallback encoded_callback_;
   base::Closure error_callback_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_MEDIA_ENCODER_H_