Add the experimental filter property to html5 externs.
@@ -902,6 +902,12 @@ function CanvasRenderingContext2D() {}
/** @const {!HTMLCanvasElement} */
CanvasRenderingContext2D.prototype.canvas;
+/**
+ * @type {string}
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/filter
+ */
+CanvasRenderingContext2D.prototype.filter;
+
/**
* @constructor
* @extends {BaseRenderingContext2D}
