Add support for proxy restrictions

Implement enforcement of the following chromium proxy restrictions:
ProxyMode, ProxyServer, ProxyBypassList

Originally cherry picked from 556a3ba3bb9dae768810181ace1e0b07fd5824c2.

Includes fix for search restriction unit test failures when
including proxy restrictions code.

Also added some logging for functional verification.

Change-Id: If7fc1d8be36fa600a3d974d6b584d504ed2faf71
3 files changed