GitLab

* Initialize ui::NetworkConnect during mash startup
* Provide a stub NetworkConnect::Delegate implementation

It still won't actually switch networks on the device (there are issues
talking to shill in lower-level code) but it's a step in the right direction.

BUG=644355
TEST=manual, click on network in system tray, no crash

Review-Url: https://codereview.chromium.org/2394503003
Cr-Commit-Position: refs/heads/master@{#423021}