[Android] Fix crash issue caused by the download listener.

This is because the XWalk core uses the request API to download
local file in the case, which would cause the crash.

So when downloading the local file, download listener would
only do the file transfer for this.

BUG=https://crosswalk-project.org/jira/browse/XWALK-338
Merge pull request #1160 from junmin-zhu/file

[Android] Fix crash issue caused by the download listener.
[Android][SysApps] 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() {...}