[Android][Extensions] Support 'onxxx' event handler for display and
storage

This commit fixes two things:
1. The type name in the addEventListener() should be 'attach' instead of
'onattach' according to the W3C spec. Same as 'detach', 'connect' and
'disconnect'.
2. Support 'onxxx' event handler, for example:
navigator.system.onattach = function() {...}