Clean up CSSParserContext arguments in property parsing code

This patch cleans up CSSParserContext arguments in the property parser,
tightening them to the CSSParserMode if possible, and replacing values
by const refs to avoid unneeded copies.

BUG=499780

Review URL: https://codereview.chromium.org/1514583004

Cr-Commit-Position: refs/heads/master@{#364289}
3 files changed