Support unknown property strings in transition-property

The spec mandates that transition-property (and thus the transition
shorthand) are able to support arbitrary unknown properties, for
backwards and forwards compatibility. This patch adds support for such
unknown properties.

Note that this makes the shorthand strings like "ease" or "ease ease-in"
ambiguous. In this patch we take the first case to refer to a timing
function, and in the second case the first token as a timing function
and the second token as the property name.

This change progresses the w3c transitions test transition-property-002,
although the first two cases of the test are incorrect.

BUG=304020,375098

Review URL: https://codereview.chromium.org/298043007

git-svn-id: svn://svn.chromium.org/blink/trunk@176489 bbb929c8-8fbe-4397-9dbb-9b2b20218538