Some blink unittests depend on common fonts which may not be available
on all platforms. This problem is solved in blink layout tests by using
custom font configuration with fonts from //third_party/test_fonts .
Previously the corresponding code was part of content_shell. Moved
it to //skia to make it possible to reuse it for blink_platform_unittests
and skia_unittests.

Bug: 928459
Change-Id: Ic7ea1e53c29ca9aea9014ed6c778ad0f8a2de6fb
Reviewed-on: https://chromium-review.googlesource.com/c/1469287Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632414}