[Cast Channel] Fix "leaky" CastChannelOpenFunction.

extensions/browser/api/cast_channel/cast_socket.h

Index: extensions/browser/api/cast_channel/cast_socket.h
diff --git a/extensions/browser/api/cast_channel/cast_socket.h b/extensions/browser/api/cast_channel/cast_socket.h
index 08a69b4bf8108467bb7c727ebfd6382f12906ed8..08932b02209497b766b28afcc4e39cee9c635427 100644
--- a/extensions/browser/api/cast_channel/cast_socket.h
+++ b/extensions/browser/api/cast_channel/cast_socket.h
@@ -70,6 +70,9 @@ class CastSocket : public ApiResource {
   // Instead use Close().
   // |callback| will be invoked with any ChannelError that occurred, or
   // CHANNEL_ERROR_NONE if successful.
+  // If the CastSocket is destroyed while the connection is pending, |callback|
+  // will be invoked with CHANNEL_ERROR_UNKNOWN. In this case, invoking

[mark a. foltz, 2017/02/21 18:30:01]

CHANNEL_ERROR_SOCKET_ERROR is used elsewhere for socket-level issues IIRC.

[imcheng, 2017/02/21 22:55:48]

socket_error is used for errors with read/write socket operations. I chose to
use unknown here since it is an edge case and it is unlikely the extension will
receive it anyway (since it is being unloaded).

+  // |callback| must not result in an re-entrancy behavior.

[mark a. foltz, 2017/02/21 18:30:01]

s/an/any/

[imcheng, 2017/02/21 22:55:48]

Done.

   // |delegate| receives message receipt and error events.
   // Ownership of |delegate| is transferred to this CastSocket.
   virtual void Connect(std::unique_ptr<CastTransport::Delegate> delegate,
@@ -323,6 +326,8 @@ class CastSocketImpl : public CastSocket {
   std::unique_ptr<CastMessage> challenge_reply_;
 
   // Callback invoked when the socket is connected or fails to connect.
+  // TODO(imcheng): Change to OnceCallback? OnceCallback is move-only which

[mark a. foltz, 2017/02/21 18:30:01]

I think the benefit is pretty slight here, not sure it's worth a TODO. 
Personally, I'll probably use the new callbacks for new code but not try to
retrofit existing code.

[imcheng, 2017/02/21 22:55:47]

Ok, removed TODO.

+  // is an issue for gmock.
   base::Callback<void(ChannelError)> connect_callback_;
 
   // Callback invoked by |connect_timeout_timer_| to cancel the connection.