Port uproxy-networking to freedom 0.6

I don't think you need to create a new promise. I think the following will work:
```typescript
// obfuscatedConnection_ doesn't exist until onceChurnSetup_ fulfills.
public onceConnected = this.onceChurnSetup_.then(() => {
  return this.obfuscatedConnection_.onceConnected.then((addresses:WebRtc.ConnectionAddresses) => {
    this.pcState = WebRtc.State.CONNECTED;
    return addresses;
  });
});
```