Change kerning & ligature tests

Change the font kerning and ligature tests to be pixel tests instead of
ref-tests as the current references are built on the assumption that no
font features are enabled for text by default. In many ways these tests
do not currently test our kerning & ligature features instead they test
the difference between the simple and complex paths.

Changing these to be pixel tests allows the tests to correctly test the
rendering of these font features.

BUG=536784
R=drott@chromium.org

Review URL: https://codereview.chromium.org/1395333002

Cr-Commit-Position: refs/heads/master@{#353492}
7 files changed