[Android] Launch Screen implementation

To support Launch Screen feature, added a new listener on
ContentViewrRenderView
The listener will be fired when web content has been rendered and
screen has been updated.

SPEC: https://docs.google.com/a/intel.com/document/d/17PuNuHRTQuREUpaCvj-eEx7uYi2avd-VW-oaMXMpvwo/edit?pli=1#
Design Doc: https://docs.google.com/a/intel.com/document/d/1YLajlZC7CkBOtEvzD6p6yeBr0HrPsaIGX8Eqhr3oTF4/edit#heading=h.mfsu3bk9566e
Bug: https://crosswalk-project.org/jira/browse/XWALK-637?filter=-1