Changed MatchedPropertiesCache to use OwnPtr.

Since CachedMatchedProperties has no traits, changed to use OwnPtr for m_cahce.

Review URL: https://chromiumcodereview.appspot.com/23568007

git-svn-id: svn://svn.chromium.org/blink/trunk@157120 bbb929c8-8fbe-4397-9dbb-9b2b20218538