Cleanup CSSPropertyParser

Remove a large number of methods from the legacy CSSPropertyParser
that are not used anymore. Also move isGeneratedImage and
createCSSImageValueWithReferrer into CSSPropertyParser.cpp.

BUG=499780

Review URL: https://codereview.chromium.org/1736763003

Cr-Commit-Position: refs/heads/master@{#380113}
3 files changed