Build WebRTC with data channel only.

webrtc/call/call.h

Index: webrtc/call/call.h
diff --git a/webrtc/call/call.h b/webrtc/call/call.h
index f67b6907e5f7a1c3465b984dc23de768f6130631..65f2294e86c3cc4ff20194f61a558f0c66881f1f 100644
--- a/webrtc/call/call.h
+++ b/webrtc/call/call.h
@@ -65,7 +65,7 @@ class Call {
       RTC_DCHECK(event_log);
     }
 
-    static const int kDefaultStartBitrateBps;
+    static const int kDefaultStartBitrateBps = 300000;

[Taylor Brandstetter, 2017/05/11 04:43:11]

Why did this have to move? Are there places that use kDefaultStartBitrateBps but
don't need the rest of Call? If so, I'd leave a TODO to fix that.

[Zhi Huang, 2017/05/12 20:05:33]

This is because call.h is an abstract class and it is part of the
"call_interface" build target while the call.cc is part of "call" target. When
building WebRTC without media, we don't build the "call" target so I have to
give the const member a value to avoid link errors. But  I'm not sure if this is
a good idea.

 
     // Bitrate config used until valid bitrate estimates are calculated. Also
     // used to cap total bitrate used.