GitLab

This CL creates a new type of KeyboardHook to listen to media keys.
KeyboardHook::Create is split in two, providing access to each type of
KeyboardHook. This creates the media hook implementation for Windows,
and returns nullptr for other platforms.

Bug: 903582
Change-Id: I5eb6bbd94ec23dd54867eeb9ced585bc1b726961
Reviewed-on: https://chromium-review.googlesource.com/c/1333118
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611500}