Support for onbufferedamountlow

talk/app/webrtc/objc/RTCDataChannel.mm

Index: talk/app/webrtc/objc/RTCDataChannel.mm
diff --git a/talk/app/webrtc/objc/RTCDataChannel.mm b/talk/app/webrtc/objc/RTCDataChannel.mm
index 4fb03c284ebbb7e2e1ca8427bfabfee882cfc54f..b8439f7b07c8761103ca5775df03ec8f09262425 100644
--- a/talk/app/webrtc/objc/RTCDataChannel.mm
+++ b/talk/app/webrtc/objc/RTCDataChannel.mm
@@ -43,6 +43,15 @@ class RTCDataChannelObserver : public DataChannelObserver {
     [_channel.delegate channelDidChangeState:_channel];
   }
 
+  void OnBufferedAmountChange(uint64 previousAmount) override {

[tkchin_webrtc, 2015/06/30 00:24:11]

nit:
this might look cleaner with a local var (and it'd be more correct too - when
accessing weak ptr twice in a row the second time may return nil while the first
doesn't).
RTCDataChannel* channel = _channel;  (converts to strong ptr)
id<RTCDataChannelDelegate> delegate = channel.delegate;
if ([delegate respondsTo....]) {
etc.
}

+    if ([_channel.delegate
+            respondsToSelector:@selector(channelDidChangeBufferedAmount:
+                                                         previousAmount:)]) {
+      [_channel.delegate channelDidChangeBufferedAmount:_channel
+                                         previousAmount:previousAmount];
+    }
+  }
+
   void OnMessage(const DataBuffer& buffer) override {
     if (!_channel.delegate) {
       return;