Support multiple text decoration styles.

Currently, we draw only the last seen text decoration style during
decoration painting, even when multiple decorations
(e.g. underline + overline) are applied. Hence, we potentially draw
the wrong decoration style for one or more of the applied decorations.

Fixed by fetching the matching style for each decoration, similar
to how the matching text-decoration-color is fetched.

BUG=351282
TEST=text-decoration-style-multiple.html

Review URL: https://codereview.chromium.org/195093002

git-svn-id: svn://svn.chromium.org/blink/trunk@168946 bbb929c8-8fbe-4397-9dbb-9b2b20218538