Move consumeImage to CSSPropertyParserHelpers

Move consumeImage to CSSPropertyParserHelpers along with
a lot of supporting code. Also rewrite consumeCursor
to start using consumeImage; as a nice side effect the
consumeCursor code becomes shorter and easier to read.

Review-Url: https://codereview.chromium.org/2200313002
Cr-Commit-Position: refs/heads/master@{#410369}
3 files changed