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

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

 // 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.
 
 #include "extensions/renderer/api/display_source/wifi_display/wifi_display_media_encoder.h"
 
 #include "base/logging.h"
 #include "media/base/bind_to_current_loop.h"
 
 namespace extensions {
@@ skipping 15 matching lines @@
     DCHECK_LE(dts, pts);
   }
 }
 
 WiFiDisplayMediaEncoder::WiFiDisplayMediaEncoder() = default;
 WiFiDisplayMediaEncoder::~WiFiDisplayMediaEncoder() = default;
 
 void WiFiDisplayMediaEncoder::SetCallbacks(
     const EncodedUnitCallback& encoded_callback,
     const base::Closure& error_callback) {
+  DCHECK(client_thread_checker_.CalledOnValidThread());
   // This is not thread-safe if encoding has been started thus allow
   // this to be called only once.
   DCHECK(encoded_callback_.is_null() && error_callback_.is_null());
   encoded_callback_ = media::BindToCurrentLoop(encoded_callback);
   error_callback_ = media::BindToCurrentLoop(error_callback);
 }
 
 }  // namespace extensions