Add support for injecting VideoBitrateAllocatorFactory also on IOS

This patch exposes webrtc::PeerConnectionDependencies c++-object
and makes it possible to supply one when creating a PeerConnection.

This makes it possible to e.g inject a VideoBitrateAllocatorFactory.

Bug: webrtc:10547
Change-Id: Ib7431bdcec1380e7903dc5f66f3583501aeab0a5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168307
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30480}

sdk/objc/api/peerconnection/RTCPeerConnectionFactory+Native.h

@@ -22,6 +22,7 @@ class NetworkControllerFactoryInterface;
 class VideoEncoderFactory;
 class VideoDecoderFactory;
 class AudioProcessing;
+struct PeerConnectionDependencies;
 
 }  // namespace webrtc
 
@@ -87,6 +88,16 @@ NS_ASSUME_NONNULL_BEGIN
                         decoderFactory:(nullable id<RTCVideoDecoderFactory>)decoderFactory
                  mediaTransportFactory:
                      (std::unique_ptr<webrtc::MediaTransportFactory>)mediaTransportFactory;
+
+/** Initialize an RTCPeerConnection with a configuration, constraints, and
+ *  dependencies.
+ */
+- (RTCPeerConnection *)
+    peerConnectionWithDependencies:(RTCConfiguration *)configuration
+                       constraints:(RTCMediaConstraints *)constraints
+                      dependencies:(std::unique_ptr<webrtc::PeerConnectionDependencies>)dependencies
+                          delegate:(nullable id<RTCPeerConnectionDelegate>)delegate;
+
 @end
 
 NS_ASSUME_NONNULL_END