ash::internal::TrayBluetooth: Hide spinner if discovery session stops.

ash::internal::TrayBluetooth: Hide spinner if discovery session stops.

Changed TrayBluetooth to update the spinner not based on whether or not it
requested discovery but whether or not system tray delegate has an active
discovery session. The code will now automatically try to restart discovery
if discovery stops unexpectedly and start or stop the throbber based on that.

Also renamed UpdateBlueToothDeviceList to UpdateBluetoothDeviceList and
UpdateBluetoothDeviceList to UpdateBluetoothDeviceListHelper.

BUG=345494
TEST=1. Hack bluetoothd to allow stopping discovery via command-line regardless
of the client who intiated it. Use bluetoothctl and run 'scan off' after running
discovery via TrayBluetooth. The spinner should visibly update and discovery
should restart (upon which the spinner should re-update).
2. Start discovery outside of TrayBluetooth (e.g chrome://settings). Opening the
tray discovery dialog should work as expected (i.e. the spinner should animate
and found devices list should be populated.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260718

[armansito, 2014-03-29 00:40:52]

jennyz@: ash/system/*
derat@: chrome/browser/ui/ash/*
keybuk@: general Bluetooth.

[Daniel Erat, 2014-03-29 00:45:34]

lgtm for chrome/browser/ui/ash

[keybuk, 2014-03-31 16:09:37]

lgtm

[jennyz, 2014-03-31 18:10:49]

lgtm

[armansito, 2014-03-31 20:52:23]

The CQ bit was checked by armansito@chromium.org

[commit-bot: I haz the power, 2014-03-31 20:53:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/armansito@chromium.org/216293007/1

[commit-bot: I haz the power, 2014-04-01 00:37:08]

Change committed as 260718