[Android] Use the same UserAgent for URLRequest when connection via websocket

Applying upstream commit 145b29d in content shell to crosswalk.

BUG=https://crosswalk-project.org/jira/browse/XWALK-3073
(cherry picked from commit d48dc2f571086ebb8df63f3104b5cb07db40e6da)
Merge pull request #2709 from wang16/ws_user_agent_10

[Android] Use the same UserAgent for URLRequest when connection via webs...