Create a new local context class.

CSSParserLocalContext represents local context for each property.
Currently it only has one boolean field (use_alias_parsing), but it
will be later extended to contain other info, such as whether the
property is a longhand of a shorthand.

BUG=668012

Review-Url: https://codereview.chromium.org/2901393002
Cr-Commit-Position: refs/heads/master@{#474897}
3 files changed