[DL]: Rename isLocked to locked as per design principle.

As https://w3ctag.github.io/design-principles/#api-surface suggests,
boolean attributes should not have "is" at the beginning of their names.

This patch fixes this for DisplayLockContext.isLocked

R=chrishtr@chromium.org

Bug: 882663, github.com/WICG/display-locking/issues/43
Change-Id: Ie5be4b4f6fd0ee8656fbb3c31aae0e7eb0fc3612
Reviewed-on: https://chromium-review.googlesource.com/c/1466155
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632467}
5 files changed