function _normalizeConstructor(input) {
        var constructorFn;

        if (input.constructor === Array) {
            //
            var injected = input.slice(0, input.length - 1);
            constructorFn = input[input.length - 1];
            constructorFn.$inject = injected;
        } else {
            constructorFn = input;
        }

        return constructorFn;
    }
If the constructorFn is an array of type ['dep1', 'dep2', ..., constructor() {}]
we need to pull out the array of dependencies and add it as an $inject property of the
actual constructor function.
@param input
@returns {*}
@private