Adding Java and Obj-C bindings for RtpEncodingParameters.ssrc.

BUG=webrtc:6903

Review-Url: https://codereview.webrtc.org/2581913002
Cr-Commit-Position: refs/heads/master@{#15936}

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

@@ -14,6 +14,7 @@
 
 @synthesize isActive = _isActive;
 @synthesize maxBitrateBps = _maxBitrateBps;
+@synthesize ssrc = _ssrc;
 
 static const int kBitrateUnlimited = -1;
 
@@ -30,6 +31,9 @@ static const int kBitrateUnlimited = -1;
       _maxBitrateBps =
           [NSNumber numberWithInt:nativeParameters.max_bitrate_bps];
     }
+    if (nativeParameters.ssrc) {
+      _ssrc = [NSNumber numberWithUnsignedLong:*nativeParameters.ssrc];
+    }
   }
   return self;
 }
@@ -40,6 +44,9 @@ static const int kBitrateUnlimited = -1;
   if (_maxBitrateBps != nil) {
     parameters.max_bitrate_bps = _maxBitrateBps.intValue;
   }
+  if (_ssrc != nil) {
+    parameters.ssrc = rtc::Optional<uint32_t>(_ssrc.unsignedLongValue);
+  }
   return parameters;
 }
 

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

@@ -25,6 +25,9 @@ RTC_EXPORT
  */
 @property(nonatomic, copy, nullable) NSNumber *maxBitrateBps;
 
+/** The SSRC being used by this encoding. */
+@property(nonatomic, readonly, nullable) NSNumber *ssrc;
+
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
 
 @end