ObjC: RTCVideoSource cleanup

RTCVideoSource was recently added in
https://codereview.webrtc.org/2745193002/. This CL addresses some post
commit feedback.

BUG=webrtc:7177

Review-Url: https://codereview.webrtc.org/2812533003
Cr-Commit-Position: refs/heads/master@{#17649}

webrtc/sdk/objc/Framework/Classes/RTCPeerConnectionFactory.mm

@@ -89,9 +89,9 @@
 }
 
 - (RTCVideoSource *)videoSource {
-  rtc::scoped_refptr<webrtc::ObjcVideoTrackSource> objc_video_track_source(
+  rtc::scoped_refptr<webrtc::ObjcVideoTrackSource> objcVideoTrackSource(
       new rtc::RefCountedObject<webrtc::ObjcVideoTrackSource>());
-  return [[RTCVideoSource alloc] initWithNativeVideoSource:objc_video_track_source];
+  return [[RTCVideoSource alloc] initWithNativeVideoSource:objcVideoTrackSource];
 }
 
 - (RTCVideoTrack *)videoTrackWithSource:(RTCVideoSource *)source

webrtc/sdk/objc/Framework/Classes/RTCVideoCapturer.m

@@ -10,19 +10,16 @@
 
 #import "WebRTC/RTCVideoCapturer.h"
 
-@implementation RTCVideoCapturer {
-  __weak id<RTCVideoCapturerDelegate> _delegate;
-}
+@implementation RTCVideoCapturer
+
+@synthesize delegate = _delegate;
 
 - (instancetype)initWithDelegate:(id<RTCVideoCapturerDelegate>)delegate {
+  NSAssert(delegate != nil, @"delegate cannot be nil");
   if (self = [super init]) {
     _delegate = delegate;
   }
   return self;
 }
 
-- (id<RTCVideoCapturerDelegate>)delegate {
-  return _delegate;
-}
-
 @end

webrtc/sdk/objc/Framework/Classes/objcvideotracksource.h

@@ -11,11 +11,12 @@
 #ifndef WEBRTC_SDK_OBJC_FRAMEWORK_CLASSES_OBJCVIDEOTRACKSOURCE_H_
 #define WEBRTC_SDK_OBJC_FRAMEWORK_CLASSES_OBJCVIDEOTRACKSOURCE_H_
 
-#import <WebRTC/RTCVideoFrame.h>
-
+#include "WebRTC/RTCMacros.h"
 #include "webrtc/base/timestampaligner.h"
 #include "webrtc/media/base/adaptedvideotracksource.h"
 
+RTC_FWD_DECL_OBJC_CLASS(RTCVideoFrame);
+
 namespace webrtc {
 
 class ObjcVideoTrackSource : public rtc::AdaptedVideoTrackSource {

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnectionFactory.h

@@ -46,6 +46,9 @@ RTC_EXPORT
 - (RTCAVFoundationVideoSource *)avFoundationVideoSourceWithConstraints:
     (nullable RTCMediaConstraints *)constraints;
 
+/** Initialize a generic RTCVideoSource. The RTCVideoSource should be passed to a RTCVideoCapturer
+ *  implementation, e.g. RTCCameraVideoCapturer, in order to produce frames.
+ */
 - (RTCVideoSource *)videoSource;
 
 /** Initialize an RTCVideoTrack with a source and an id. */

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoCapturer.h

@@ -15,14 +15,17 @@ NS_ASSUME_NONNULL_BEGIN
 @class RTCVideoCapturer;
 
 RTC_EXPORT
-
-@protocol RTCVideoCapturerDelegate
+@protocol RTCVideoCapturerDelegate <NSObject>
 - (void)capturer:(RTCVideoCapturer *)capturer didCaptureVideoFrame:(RTCVideoFrame *)frame;
 @end
 
+RTC_EXPORT
 @interface RTCVideoCapturer : NSObject
-- (instancetype)initWithDelegate:(id<RTCVideoCapturerDelegate>)delegate;
+
 @property(nonatomic, readonly, weak) id<RTCVideoCapturerDelegate> delegate;
+
+- (instancetype)initWithDelegate:(id<RTCVideoCapturerDelegate>)delegate;
+
 @end
 
 NS_ASSUME_NONNULL_END

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoSource.h

@@ -18,13 +18,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 RTC_EXPORT
 
-@interface RTCVideoSource : RTCMediaSource<RTCVideoCapturerDelegate>
+@interface RTCVideoSource : RTCMediaSource <RTCVideoCapturerDelegate>
 
 - (instancetype)init NS_UNAVAILABLE;
 
-// RTCVideoCapturerDelegate protocol implementation.
-- (void)capturer:(RTCVideoCapturer*)capturer didCaptureVideoFrame:(RTCVideoFrame*)frame;
-
 /**
  * Calling this function will cause frames to be scaled down to the
  * requested resolution. Also, frames will be cropped to match the