Reland of "Revert of Update the BWE when the network route changes.

webrtc/p2p/base/port.h

Index: webrtc/p2p/base/port.h
diff --git a/webrtc/p2p/base/port.h b/webrtc/p2p/base/port.h
index 06231ecd3954db1fef1ca98c84d9a4907a808300..553223965639b09ed39157e63f8c94e394833a04 100644
--- a/webrtc/p2p/base/port.h
+++ b/webrtc/p2p/base/port.h
@@ -461,6 +461,11 @@
   bool active() const {
     return write_state_ != STATE_WRITE_TIMEOUT;
   }
+  virtual bool ReadyToSendMedia() const {
+    return write_state_ == STATE_WRITABLE ||
+           write_state_ == STATE_WRITE_UNRELIABLE;
+  }
+
   // A connection is dead if it can be safely deleted.
   bool dead(int64_t now) const;