Add file capturer to AppRTCMobile on simulator.

To achieve this, the CL does the following
- Adds sample mp4 video
- Refactors the existing RTCFileVideoCapturer to achieve continious
capture and adds tests.

Bug: webrtc:8406
Change-Id: Ibc0891176c58ec9053b42e340d2113036e7199ec
Reviewed-on: https://webrtc-review.googlesource.com/12180
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Daniela Jovanoska Petrenko <denicija@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20598}

sdk/objc/Framework/Classes/PeerConnection/RTCFileVideoCapturer.h

@@ -1,26 +0,0 @@
-/*
- *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#import <Foundation/Foundation.h>
-#import <WebRTC/RTCVideoCapturer.h>
-
-/**
- * RTCVideoCapturer that reads buffers from file.
- *
- * Per design, the file capturer can only be run once and once stopped it cannot run again.
- * To run another file capture session, create new instance of the class.
- */
-NS_CLASS_AVAILABLE_IOS(10)
-@interface RTCFileVideoCapturer : RTCVideoCapturer
-
-- (void)startCapturingFromFileNamed:(NSString *)nameOfFile;
-- (void)stopCapture;
-
-@end