Chrome OS network metrics update

Chrome OS network metrics update

Add histogram "Network.Shill.DeviceRemovedEvent" for tracking device
removed events per device (technology) type.

Add histogram "Network.Shill.Cellular.DevicePresenceStatus",
"Network.Shill.Ethernet.DevicePresenceStatus",
"Network.Shill.Wifi.DevicePresenceStatus", and
"Network.Shill.Wimax.DevicePresenceStatus" for tracking the presence
of each network device in the system. The presence status is emitted once
every 3 minutes for each device type.

While here, update the value definitions for NetworkServiceError enum to
match the definitions used in Shill. Also correct the histogram name for
WiMax related histograms.

BUG=chromium:411512, chromium:411510, chromium:402202

Review URL: https://codereview.chromium.org/589233003

Cr-Commit-Position: refs/heads/master@{#296223}