Fix MediaObserver notifications in MediaStreamManager.

This CL fixes the stream type used to notify MediaObserver about
cancelled MediaStream requests.

Before this CL, NUM_MEDIA_TYPES was used as stream type to indicate
that all stream types should be cancelled.
However, the MediaObserver end does not interpret NUM_MEDIA_TYPES this
way and the request to update the UI is ignored.

This CL sends a separate notification for each stream type so that the
UI actually gets updated for all stream types in use.

Bug: 816033
Change-Id: Ib7d3b3046d1dd0976627f8ab38abf086eacc9405
Reviewed-on: https://chromium-review.googlesource.com/939630
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540122}
  void CreateUIRequest(const std::string& requested_audio_device_id,
                       const std::string& requested_video_device_id) {
    DCHECK(!ui_request_);
    target_process_id_ = requesting_process_id;
    target_frame_id_ = requesting_frame_id;
    ui_request_.reset(new MediaStreamRequest(
        requesting_process_id, requesting_frame_id, page_request_id,
        security_origin.GetURL(), user_gesture, request_type,
        requested_audio_device_id, requested_video_device_id, audio_type_,
        video_type_, controls.disable_local_echo));
  }

  void CreateUIRequest(const std::string& requested_audio_device_id,
                       const std::string& requested_video_device_id) {
    DCHECK(!ui_request_);
    target_process_id_ = requesting_process_id;
    target_frame_id_ = requesting_frame_id;
    ui_request_.reset(new MediaStreamRequest(
        requesting_process_id, requesting_frame_id, page_request_id,
        security_origin.GetURL(), user_gesture, request_type,
        requested_audio_device_id, requested_video_device_id, audio_type_,
        video_type_, controls.disable_local_echo));
  }
