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This CL contains a base class and unittests for generating
a keyboard layout map for the KeyboardMap API.  It also
includes a a Windows implementation which uses the base
class.

BUG=832811

Change-Id: I7ff20cf8b2a34cf8c7a9bbe9609e40f39bb89634
Reviewed-on: https://chromium-review.googlesource.com/1077596
Commit-Queue: Joe Downing <joedow@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Gary Kacmarcik <garykac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564918}