Fixes a test in gfx_unittests that fails on Windows only.
Fixes a test in gfx_unittests that fails on Windows only.

BUG=587223

Review URL: https://codereview.chromium.org/1705243003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#377183}

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