Add ability to mark video sources for screen casting in ObjC

Bug: webrtc:13033
Change-Id: If30a4889cd2cb0ecc5ee91eed2ee9b496a40c852
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227295
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34818}

sdk/objc/api/peerconnection/RTCPeerConnectionFactory.h

@@ -60,6 +60,13 @@ RTC_OBJC_EXPORT
  */
 - (RTC_OBJC_TYPE(RTCVideoSource) *)videoSource;
 
+/** Initialize a generic RTCVideoSource with he posibility of marking
+ * it as usable for screen sharing. The RTCVideoSource should be
+ * passed to a RTCVideoCapturer implementation, e.g.
+ * RTCCameraVideoCapturer, in order to produce frames.
+ */
+- (RTC_OBJC_TYPE(RTCVideoSource) *)videoSourceForScreenCast:(BOOL)forScreenCast;
+
 /** Initialize an RTCVideoTrack with a source and an id. */
 - (RTC_OBJC_TYPE(RTCVideoTrack) *)videoTrackWithSource:(RTC_OBJC_TYPE(RTCVideoSource) *)source
                                                trackId:(NSString *)trackId;

sdk/objc/api/peerconnection/RTCPeerConnectionFactory.mm

@@ -247,6 +247,13 @@
                                                    workerThread:_workerThread.get()];
 }
 
+- (RTC_OBJC_TYPE(RTCVideoSource) *)videoSourceForScreenCast:(BOOL)forScreenCast {
+  return [[RTC_OBJC_TYPE(RTCVideoSource) alloc] initWithFactory:self
+                                                signalingThread:_signalingThread.get()
+                                                   workerThread:_workerThread.get()
+                                                   isScreenCast:forScreenCast];
+}
+
 - (RTC_OBJC_TYPE(RTCVideoTrack) *)videoTrackWithSource:(RTC_OBJC_TYPE(RTCVideoSource) *)source
                                                trackId:(NSString *)trackId {
   return [[RTC_OBJC_TYPE(RTCVideoTrack) alloc] initWithFactory:self source:source trackId:trackId];

sdk/objc/api/peerconnection/RTCVideoSource+Private.h

@@ -41,6 +41,11 @@ NS_ASSUME_NONNULL_BEGIN
                 signalingThread:(rtc::Thread *)signalingThread
                    workerThread:(rtc::Thread *)workerThread;
 
+- (instancetype)initWithFactory:(RTC_OBJC_TYPE(RTCPeerConnectionFactory) *)factory
+                signalingThread:(rtc::Thread *)signalingThread
+                   workerThread:(rtc::Thread *)workerThread
+                   isScreenCast:(BOOL)isScreenCast;
+
 @end
 
 NS_ASSUME_NONNULL_END

sdk/objc/api/peerconnection/RTCVideoSource.mm

@@ -51,8 +51,18 @@ static webrtc::ObjCVideoTrackSource *getObjCVideoSource(
 - (instancetype)initWithFactory:(RTC_OBJC_TYPE(RTCPeerConnectionFactory) *)factory
                 signalingThread:(rtc::Thread *)signalingThread
                    workerThread:(rtc::Thread *)workerThread {
+  return [self initWithFactory:factory
+               signalingThread:signalingThread
+                  workerThread:workerThread
+                  isScreenCast:NO];
+}
+
+- (instancetype)initWithFactory:(RTC_OBJC_TYPE(RTCPeerConnectionFactory) *)factory
+                signalingThread:(rtc::Thread *)signalingThread
+                   workerThread:(rtc::Thread *)workerThread
+                   isScreenCast:(BOOL)isScreenCast {
   rtc::scoped_refptr<webrtc::ObjCVideoTrackSource> objCVideoTrackSource(
-      new rtc::RefCountedObject<webrtc::ObjCVideoTrackSource>());
+      new rtc::RefCountedObject<webrtc::ObjCVideoTrackSource>(isScreenCast));
 
   return [self initWithFactory:factory
              nativeVideoSource:webrtc::VideoTrackSourceProxy::Create(

sdk/objc/native/src/objc_video_track_source.h

@@ -27,10 +27,9 @@ namespace webrtc {
 class ObjCVideoTrackSource : public rtc::AdaptedVideoTrackSource {
  public:
   ObjCVideoTrackSource();
+  explicit ObjCVideoTrackSource(bool is_screencast);
   explicit ObjCVideoTrackSource(RTCObjCVideoSourceAdapter* adapter);
 
-  // This class can not be used for implementing screen casting. Hopefully, this
-  // function will be removed before we add that to iOS/Mac.
   bool is_screencast() const override;
 
   // Indicates that the encoder should denoise video before encoding it.
@@ -52,6 +51,7 @@ class ObjCVideoTrackSource : public rtc::AdaptedVideoTrackSource {
   rtc::TimestampAligner timestamp_aligner_;
 
   RTCObjCVideoSourceAdapter* adapter_;
+  bool is_screencast_;
 };
 
 }  // namespace webrtc

sdk/objc/native/src/objc_video_track_source.mm

@@ -34,15 +34,18 @@
 
 namespace webrtc {
 
-ObjCVideoTrackSource::ObjCVideoTrackSource()
+ObjCVideoTrackSource::ObjCVideoTrackSource() : ObjCVideoTrackSource(false) {}
-    : AdaptedVideoTrackSource(/* required resolution alignment */ 2) {}
+
+ObjCVideoTrackSource::ObjCVideoTrackSource(bool is_screencast)
+    : AdaptedVideoTrackSource(/* required resolution alignment */ 2),
+      is_screencast_(is_screencast) {}
 
 ObjCVideoTrackSource::ObjCVideoTrackSource(RTCObjCVideoSourceAdapter *adapter) : adapter_(adapter) {
   adapter_.objCVideoTrackSource = this;
 }
 
 bool ObjCVideoTrackSource::is_screencast() const {
-  return false;
+  return is_screencast_;
 }
 
 absl::optional<bool> ObjCVideoTrackSource::needs_denoising() const {