[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
(cherry picked from commit e8aea8eaa530754eb4fd89fb8ddf8d306b888097)
Merge pull request #2492 from wang16/crosswalk-9

[Android] Bring back enableRemoteDebugging API temporally