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Since other methods separate supported binary image MIME types from SVG,
where SVG was detected as a "non image type" along with XML, and since I
needed a method to detect MIME types that can be displayed as an image,
I've added such a method.

BUG=398443

Review URL: https://codereview.chromium.org/471913002

Cr-Commit-Position: refs/heads/master@{#291750}