toMatchSelector = function (expected) {
        return this.actual.selector.trim() === expected;
    }
Verifies whether one of the results returned by CSSUtils._findAllMatchingSelectorsInText()
came from the expected selector string or not. String is the complete compound selector, not
the larger selector group or the smaller rightmost-simple-selector. E.g. if some rule
"div, foo .bar { ... }" matches a search for ".bar", the selector will be "foo .bar"