Move classes in the device.usb Mojo namespace to device.mojom

The USB Mojo service was added before there was clear guidance on what
namespace Mojo modules should use. The convention is now to use
foo.mojom.

The USB Mojo service implementation is still in the device::usb
namespace which violates the general Chromium style guide recommendation
to not use nested namespaces. This will be fixed in a later patch.

BUG=699790

Review-Url: https://codereview.chromium.org/2821723002
Cr-Commit-Position: refs/heads/master@{#465467}
44 files changed