[chrome.displaySource] Use a scoped enumeration for initialization steps.

extensions/renderer/api/display_source/wifi_display/wifi_display_media_pipeline.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_PIPELINE_H_
 #define EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_MEDIA_PIPELINE_H_
 
 #include <memory>
 #include <string>
 #include <utility>
@@ skipping 43 matching lines @@
   void InsertRawVideoFrame(
       const scoped_refptr<media::VideoFrame>& video_frame,
       base::TimeTicks reference_time);
 
   void RequestIDRPicture();
 
   WiFiDisplayAudioEncoder* audio_sink() { return audio_encoder_.get(); }
 
  private:
   using InitStepCompletionCallback = InitCompletionCallback;
-  enum InitializationStep : unsigned;
+  enum class InitializationStep : unsigned;
 
   WiFiDisplayMediaPipeline(
       wds::SessionType type,
       const WiFiDisplayVideoEncoder::InitParameters& video_parameters,
       const wds::AudioCodec& audio_codec,
       const std::string& sink_ip_address,
       const std::pair<int, int>& sink_rtp_ports,
       const RegisterMediaServiceCallback& service_callback,
       const ErrorCallback& error_callback);
 
@@ skipping 30 matching lines @@
   WiFiDisplayMediaServicePtr media_service_;
 
   base::WeakPtrFactory<WiFiDisplayMediaPipeline> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WiFiDisplayMediaPipeline);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_MEDIA_PIPELINE_H_