Introduced blink::mojom::WebUsbService with restricted methods.

This CL introduced blink::mojom::WebUsbService implemented
by WebUsbServiceImpl in chrome/browser/usb which used to be
WebDeviceManager.
Paralleling with device::mojom::UsbDeviceManager, the new interface
aims to simplify the interactions with Blink, and a meaningless
argument of GetDevices() method has been reduced in this CL.
device::mojom::UsbChooserService will be merged to this interface in
subsequent CLs.

BUG=699790

Change-Id: I891c56460425c20d2e8d067f9335091f6945ae7d
Reviewed-on: https://chromium-review.googlesource.com/1151065
Commit-Queue: Donna Wu <donna.wu@intel.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582108}
29 files changed