Unit tests shouldn't use bloatedCharacters()

We're getting down to just a few callers of bloatedCharacters(). This CL
removes some callers in unit tests so I can more easily see the remaining
callers.

R=pdr
BUG=254708

Review URL: https://chromiumcodereview.appspot.com/19311002

git-svn-id: svn://svn.chromium.org/blink/trunk@154304 bbb929c8-8fbe-4397-9dbb-9b2b20218538