Migrate Chrome OS Bluetooth UI to the new discovery API.

This CL migrates BluetoothOptionsHandler and ash::SystemTrayDelegate to the
new discovery session API, removing calls to the now deprecated
device::BluetoothAdapter::Start|StopDiscovering.

BUG=346982
TEST=Tested that discovery logic works on Uber tray and chrome://settings. Opened
multiple tabs with chrome://settings/search#Bluetooth. Also tested that all
BluetoothDiscoverySession objects are marked as inactive when the adapter gets
powered down via bt_console.

Review URL: https://codereview.chromium.org/184953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254727 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254727
Disable memory performance_ui_test.

This will drop some coverage because the Telemetry replacement
doesn't exercise the exact scenario that this did. However, it
is brokens, scheduled for decommision and not worth fixing.

BUG=347340,237694

Review URL: https://codereview.chromium.org/186263004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254728 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254728