[Android] Enable the internal extension in the embedded mode.

Copy the js wrapper into the xwalk_app_template target, which
would be used by the web app when packaged in embedded mode.

BUG=https://crosswalk-project.org/jira/browse/XWALK-615
Merge pull request #1232 from junmin-zhu/internalAPI

[Android] Enable the internal extension in the embedded mode.