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The check for GTK 3.20 was incorrect as the issue it was trying to fix
was still occurring on GTK 3.20+ systems.  This CL adds the correct,
but more complex, check.

Verified on these configurations:
{GTK 3.18, GTK 3.22} X
{Breeze, Adwaita, OSX-Arc-White, Greybird} X
{scale=1, scale=2} X
{fullscreen, restored}

BUG=821881
R=thestig

Change-Id: I05afa35c1452a46a1abf4c39191a13657bfd8e2c
Reviewed-on: https://chromium-review.googlesource.com/990717Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547921}