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Original change's description:
> MediaLicenses can be cleared from the ClearBrowsingData dialog, so update the
> BrowsingDataRemoverBrowserTest to check them as well. This uses the test-only
> External Clear Key CDM to store the license in the file system, if it is
> available.

This reverts commit e9fc38c7.

The original CL was flaky due to Mac's only saving file timestamps to
second granularity. As a result it was possible for the newly created license
to be saved with a timestamp prior to the current actual time, and deleting
"old" licenses would include it in the deletion. Change is to wait for some
time on Macs only to ensure that the "new" license has a later timestamp.

BUG=808690,879812
TEST=new browser_tests pass

Change-Id: Ibd7cf65b468f98af9aa583d3f320e54c8f3f223e
Reviewed-on: https://chromium-review.googlesource.com/c/1345248Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610211}