Revert API change from issue 1053883002.
Revert API change from issue 1053883002.

tl;dr is that unless the Proxy is passed, the caller doesn't know
whether it's a Stub or Proxy (or whether it's bound).

See that patch for further explanation.

BUG=
R=hansmuller@google.com

Review URL: https://codereview.chromium.org/1052693003

collinjackson/mojo,collinjackson/mojo,collinjackson/mojo,collinjackson/mojo,chinmaygarde/mojo,jianglu/mojo,afandria/mojo,afandria/mojo,afandria/mojo,jianglu/mojo,afandria/mojo,afandria/mojo,jianglu/mojo,collinjackson/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,afandria/mojo,jianglu/mojo,jianglu/mojo,chinmaygarde/mojo,jianglu/mojo,chinmaygarde/mojo,chinmaygarde/mojo,chinmaygarde/mojo,collinjackson/mojo,collinjackson/mojo,chinmaygarde/mojo,jianglu/mojo,collinjackson/mojo,chinmaygarde/mojo,collinjackson/mojo,chinmaygarde/mojo,afandria/mojo