Prevent FontSizes::Ex conversion when we have no font

Bug: 801931
Change-Id: Ie76b4a5525537c1888be82b56a82dd4accf27eeb
Reviewed-on: https://chromium-review.googlesource.com/1072268
Commit-Queue: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562851}
10 files changed