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Switches all remaining uses of expected colors in the GPU pixel tests to
regular pixel tests. Initially, these are set to use the very permissive
Sobel algorithm so that images are auto-triaged until enough data is
collected to calculate suitable less permissive parameters. The tests
have grace periods defined until June 22nd, so any flakes that are not
caught by the permissive algorithm will not affect the bots.

Bug: 1078914
Change-Id: Ia59bba2d5117b66a537b4be3894cc9b2725ead56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219585
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773911}