Support multiple bindings in device::usb::DeviceManagerImpl.

Support multiple bindings in DeviceManagerImpl so that the Device
Service can own a unique DeviceManagerImpl instance easily and
the unique UsbService instance will be owned by DeviceManagerImpl,
then we can git rid of DeviceClient after all users being converted
to mojom interface.

Bug: 699790
Change-Id: I8a62739796f99a98bf87a1ed71562c09cba9e050
Reviewed-on: https://chromium-review.googlesource.com/1221475
Commit-Queue: Donna Wu <donna.wu@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592706}
4 files changed