[Android] Support shared library mode for XWalkRuntime in WindowAndroid.

XWalkRuntime in shared mode requires WindowAndroid to have a share library context
to get resources in shared library. Add constructor in WindowAndroid to make it work.

BUG=https://github.com/crosswalk-project/crosswalk/issues/678 , 666
Merge pull request #64 from sqliu/otcshare-support-share-in-window

[Android] Support shared library mode for XWalkRuntime in WindowAndroid.