[chrome.displaySource] Add a base class for audio and video encoders.

extensions/renderer/api/display_source/wifi_display/wifi_display_video_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_video_encoder.h"
 
-#include "media/base/bind_to_current_loop.h"
-
 namespace extensions {
 
-using InitParameters = WiFiDisplayVideoEncoder::InitParameters;
-using VideoEncoderCallback = WiFiDisplayVideoEncoder::VideoEncoderCallback;
-
 WiFiDisplayVideoEncoder::InitParameters::InitParameters() = default;
 WiFiDisplayVideoEncoder::InitParameters::InitParameters(const InitParameters&) =
     default;
 WiFiDisplayVideoEncoder::InitParameters::~InitParameters() = default;
 
 WiFiDisplayVideoEncoder::WiFiDisplayVideoEncoder() = default;
 WiFiDisplayVideoEncoder::~WiFiDisplayVideoEncoder() = default;
 
-void WiFiDisplayVideoEncoder::SetCallbacks(
-    const EncodedFrameCallback& encoded_callback,
-    const base::Closure& error_callback) {
-  encoded_callback_ = media::BindToCurrentLoop(encoded_callback);
-  error_callback_ = media::BindToCurrentLoop(error_callback);
-}
-
+// static
 void WiFiDisplayVideoEncoder::Create(
     const InitParameters& params,
     const VideoEncoderCallback& encoder_callback) {
   NOTIMPLEMENTED();
   encoder_callback.Run(nullptr);
 }
 
 }  // namespace extensions