Add degradationPreference to RTCRtpParameters in ObjC SDK.

Bug: None
Change-Id: I64daf9ac142f960a13f9e69705ba8d3b865578e0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/164527
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Mirta Dvornicic <mirtad@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30164}

sdk/objc/api/peerconnection/RTCRtpParameters.h

@@ -18,6 +18,14 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+/** Corresponds to webrtc::DegradationPreference. */
+typedef NS_ENUM(NSInteger, RTCDegradationPreference) {
+  RTCDegradationPreferenceDisabled,
+  RTCDegradationPreferenceMaintainFramerate,
+  RTCDegradationPreferenceMaintainResolution,
+  RTCDegradationPreferenceBalanced
+};
+
 RTC_OBJC_EXPORT
 @interface RTCRtpParameters : NSObject
 
@@ -36,6 +44,12 @@ RTC_OBJC_EXPORT
 /** The negotiated set of send codecs in order of preference. */
 @property(nonatomic, copy) NSArray<RTCRtpCodecParameters *> *codecs;
 
+/**
+ * Degradation preference in case of CPU adaptation or constrained bandwidth.
+ * If nil, implementation default degradation preference will be used.
+ */
+@property(nonatomic, copy) NSNumber *degradationPreference;
+
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
 
 @end