[Android] Fix XWALK unable to support download behavior

BUG=https://crosswalk-project.org/jira/browse/XWALK-1079
@wang16 The change is not from upstream, I debugged and found the solution by myself.
The story is Content is using MSG_ROUTING_NONE for render_frame_id.  Previous implementation fails to find IoThreadClientData for it. Current change will ignore MSG_ROUTING_NONE..