Don't notify isolated processes about proxy updates.

ConnectivityManager is not accessible from isolated processes, so
notifying them causes exception logspam. Since they don't have network
privileges anyway, just don't notify them about proxy changes.

Change-Id: Ic7280df84d7f54433a03e10e998e90d48da0f562
Fixes: 64640552
Test: set proxy on wifi network, disable wifi, launch webview app, enable wifi