Use const UsbDeviceInfo reference for UsbChooserContext::Observer.

This CL made |device_info| parameter to UsbChooserContext::observer
a const device::mojom::UsbDeviceInfo& to reduce wasted clones.

Bug: 699790
Change-Id: Id9b670fab75b185fd2a55e4832e5d92cb6479aa7
Reviewed-on: https://chromium-review.googlesource.com/1249738
Commit-Queue: Donna Wu <donna.wu@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595340}
6 files changed