Break the CSS dependency in platform/SimpleFontData

To break a dependency on CSSFontFaceSource in SimpleFontData, we
move the CustomFontData class out of SimpleFontData into its
own class, and enable subclassing for CSS and SVG font
information. This also removes the AdditionalFontData class.

R=eseidel@chromium.org,eae@chromium.org
BUG=303332

Review URL: https://codereview.chromium.org/60083003

git-svn-id: svn://svn.chromium.org/blink/trunk@161461 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactoring markers-input-type-text.html to use async path for spellcheck

Use asynchronous spellchecking in markers-input-type-text.html.
In addition, remove unnecessary elements that are automatically
created by js-test.js
Use the same misspelled word 'zz' for each element to simplify
the test.
Fill in misspellings for non DumpRenderTree launchers.

BUG=295722

Review URL: https://codereview.chromium.org/60663005

git-svn-id: svn://svn.chromium.org/blink/trunk@161462 bbb929c8-8fbe-4397-9dbb-9b2b20218538