Reland "Add file capturer to AppRTCMobile on simulator."

This is a reland of 5adcd198752b651f7b7e9199a91f9b873b7d7237
Original change's description:
> 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}

Bug: webrtc:8406
Change-Id: I93be89b86e342a9a8195e19ebaf4aef1410d2c20
Reviewed-on: https://webrtc-review.googlesource.com/23200
Reviewed-by: Daniela Jovanoska Petrenko <denicija@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Daniela Jovanoska Petrenko <denicija@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20870}
diff --git a/sdk/objc/Framework/Headers/WebRTC/RTCFileVideoCapturer.h b/sdk/objc/Framework/Headers/WebRTC/RTCFileVideoCapturer.h
new file mode 100644
index 0000000..7b898e4
--- /dev/null
+++ b/sdk/objc/Framework/Headers/WebRTC/RTCFileVideoCapturer.h
@@ -0,0 +1,50 @@
+/*
+ *  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>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * Error passing block.
+ */
+typedef void (^RTCFileVideoCapturerErrorBlock)(NSError *error);
+
+/**
+ * Captures buffers from bundled video file.
+ *
+ * See @c RTCVideoCapturer for more info on capturers.
+ */
+RTC_EXPORT
+
+NS_CLASS_AVAILABLE_IOS(10)
+@interface RTCFileVideoCapturer : RTCVideoCapturer
+
+/**
+ * Starts asynchronous capture of frames from video file.
+ *
+ * Capturing is not started if error occurs. Underlying error will be
+ * relayed in the errorBlock if one is provided.
+ * Successfully captured video frames will be passed to the delegate.
+ *
+ * @param nameOfFile The name of the bundled video file to be read.
+ * @errorBlock block to be executed upon error.
+ */
+- (void)startCapturingFromFileNamed:(NSString *)nameOfFile
+                            onError:(__nullable RTCFileVideoCapturerErrorBlock)errorBlock;
+
+/**
+ * Immediately stops capture.
+ */
+- (void)stopCapture;
+@end
+
+NS_ASSUME_NONNULL_END