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This change moves the KeyboardLock API methods to a 'keyboard'
namespace on the Navigator object.  We are doing this work now as
there has been a request for additional keyboard functionality that
would also be placed on the new keyboard object and we wanted to
move the KeyboardLock methods there for consistency before we launch.

KeyboardLock API Spec is here:
https://w3c.github.io/keyboard-lock/#API

Old calling pattern:
Navigator.keyboardLock();
Navigator.keyboardUnlock();

New calling pattern:
Navigator.keyboard.lock();
Navigator.keyboard.unlock();

Note: The main logic in the KeyboardLock.cpp class and tests is the
same as it was, however the file changed enough that git does not
recognize it as a file move.

BUG=680809

Change-Id: I234b2ab12d5ecd44c894ed5103863fd96fd548d4
Reviewed-on: https://chromium-review.googlesource.com/969656Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Gary Kacmarcik <garykac@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544996}