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This CL moves BluetoothDetailedView from tray_bluetooth.cc to
a dedicated bluetooth_detailed_view.cc.

TrayBluetooth will be removed with UnifiedSystemTray, but
BluetoothDetailedView will remain.

TEST=ash_unittests, manual
BUG=none

Change-Id: I759e4882d3b5aadbfaf274127960a1795a207696
Reviewed-on: https://chromium-review.googlesource.com/1073170Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563119}