Missing Polymer.instanceof and Polymer.isInstance declarations

[kwaclaw]

These two members are not really documented but have been there since release 1.0.7 and have been mentioned in Rob Dodson's Polycast#52.

They are mentioned in the release notes for 1.0.7: https://www.polymer-project.org/1.0/docs/release-notes and here is the issue for reference: Polymer/polymer#2083 .

This seems to work for me, but I don't think it is the proper typing:

declare var Polymer: {
    (prototype: polymer.Element): FunctionConstructor;
    Class(prototype: polymer.Element): Function;
    dom: polymer.dom;
    instanceof(obj: any, ctor: any): boolean;
    isInstance(obj: any): boolean;
    appendChild(node: HTMLElement): HTMLElement;
    insertBefore(node: HTMLElement, beforeNode: HTMLElement): HTMLElement;
    removeChild(node: HTMLElement): HTMLElement;
    updateStyles(): void;
    Base: any;
};