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This was a subclass purely because WindowTargeter implements
EventTargeter functions in a protected block. Given it is expected
that WindowTargeter is an EventTargeter and EventTargeter is not an
implementation detail it seems the overrides should be in the public
section.

BUG=none
TEST=none

Change-Id: Ib93232ad50a072a63a4beb982e9f265a606b6cbe
Reviewed-on: https://chromium-review.googlesource.com/544680Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481873}