Fix serialization of content property to always quote

Fix serialization of content property to always quote
by splitting CSS_STRING into CSS_CUSTOM_IDENT (quoted
if needed) and CSS_STRING (always quoted).
Also make the CSS properties that support <string> or
<custom-ident> construct CSSPrimitiveValues with the
correct keyword(CSS_STRING/CSS_CUSTOM_IDENT), specifically
-webkit-locale, -webkit-hyphenate and -webkit-highlight
now always quote, hence a lot of tests are rebaselined.

BUG=462031

Review URL: https://codereview.chromium.org/973623002

git-svn-id: svn://svn.chromium.org/blink/trunk@191396 bbb929c8-8fbe-4397-9dbb-9b2b20218538
58 files changed