[Android] Bring back enableRemoteDebugging API temporally

Some embedders needs to get the web socket url for remote
debugging their app. The legacy API enableRemoteDebugging
returns the url but it is inaccessible.
Bring it back before the new API to get the debugging url
available.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2689
Merge pull request #2484 from wang16/remote_debugging

[Android] Bring back enableRemoteDebugging API temporally