Add getConfiguration method to USBDevice.

This allows a site to determine the current configuration state of a
device. WebUSBDevice::getConfiguration is left as non-pure until
Chromium provides an implementation.

BUG=492204

Review URL: https://codereview.chromium.org/1352283005

git-svn-id: svn://svn.chromium.org/blink/trunk/public@202621 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed