Increase tolerance for tab-size test.
Increase tolerance for tab-size test.

When the patch to switch line layout to LayoutUnits lands, it will
be possible (and acceptable) for these measurements to differ by
up to one LayoutUnit (0.015625).

R=eae@chromium.org,hartmanng@chromium.org
BUG=

Review URL: https://codereview.chromium.org/957053002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@190892 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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