Change complex-text-missing-glyph-fallback to have fixed line height

Change the fast/text/international/complex-text-missing-glyph-fallback
.html test to have a fixed line height to account for differences
between fonts.

BUG=378610
TBR=leviw@chromium.org

Review URL: https://codereview.chromium.org/336603004

git-svn-id: svn://svn.chromium.org/blink/trunk@176053 bbb929c8-8fbe-4397-9dbb-9b2b20218538