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}

examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m

@@ -11,9 +11,11 @@
 #import "ARDVideoCallViewController.h"
 
 #import "WebRTC/RTCAudioSession.h"
+#import "WebRTC/RTCCameraVideoCapturer.h"
 
 #import "ARDAppClient.h"
 #import "ARDCaptureController.h"
+#import "ARDFileCaptureController.h"
 #import "ARDSettingsModel.h"
 #import "ARDVideoCallView.h"
 #import "WebRTC/RTCAVFoundationVideoSource.h"
@@ -32,6 +34,7 @@
   ARDAppClient *_client;
   RTCVideoTrack *_remoteVideoTrack;
   ARDCaptureController *_captureController;
+  ARDFileCaptureController *_fileCaptureController NS_AVAILABLE_IOS(10);
   AVAudioSessionPortOverride _portOverride;
 }
 
@@ -101,6 +104,14 @@
   [_captureController startCapture];
 }
 
+- (void)appClient:(ARDAppClient *)client
+    didCreateLocalFileCapturer:(RTCFileVideoCapturer *)fileCapturer {
+  if (@available(iOS 10, *)) {
+    _fileCaptureController = [[ARDFileCaptureController alloc] initWithCapturer:fileCapturer];
+    [_fileCaptureController startCapture];
+  }
+}
+
 - (void)appClient:(ARDAppClient *)client
     didReceiveLocalVideoTrack:(RTCVideoTrack *)localVideoTrack {
 }
@@ -187,6 +198,8 @@
   _videoCallView.localVideoView.captureSession = nil;
   [_captureController stopCapture];
   _captureController = nil;
+  [_fileCaptureController stopCapture];
+  _fileCaptureController = nil;
   [_client disconnect];
   [_delegate viewControllerDidFinish:self];
 }