CSS Parser: Remove unneeded String object when parsing classes and ids
CSS Parser: Remove unneeded String object when parsing classes and ids

This patch fixes up consumeClass and consumeId, removing an unneeded
creation of String objects. Previously a parser token's value was a
String, but crrev.com/990083002 changed this to a CSSParserString
without updating this code.

This appears to improves the parser's performance (on some arbitrary
set of CSS files) by about 2%.

BUG=455064

Review URL: https://codereview.chromium.org/1013083002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@191979 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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