Add method on AVFoundation capturer to adapt output format.

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

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h
index 2a732b9686b877644541814da1d6a025611362d3..254196d9e1614616319516ee37ca008011324d4f 100644
--- a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCAVFoundationVideoSource.h
@@ -29,6 +29,16 @@ RTC_EXPORT
 
 - (instancetype)init NS_UNAVAILABLE;
 
+/**
+ * Calling this function will cause frames to be scaled down to the
+ * requested resolution. Also, frames will be cropped to match the
+ * requested aspect ratio, and frames will be dropped to match the
+ * requested fps. The requested aspect ratio is orientation agnostic and
+ * will be adjusted to maintain the input orientation, so it doesn't
+ * matter if e.g. 1280x720 or 720x1280 is requested.
+ */
+- (void)adaptOutputFormatToWidth:(int)width height:(int)height fps:(int)fps;
+
 /** Returns whether rear-facing camera is available for use. */
 @property(nonatomic, readonly) BOOL canUseBackCamera;