Fix #655: createPattern() can return null

PR: #677

source

@@ -59921,7 +59921,7 @@ interface <dfn>CanvasFillStrokeStyles</dfn> {
   attribute (DOMString or CanvasGradient or CanvasPattern) <span data-x="dom-context-2d-fillStyle">fillStyle</span>; // (default black)
   <span>CanvasGradient</span> <span data-x="dom-context-2d-createLinearGradient">createLinearGradient</span>(double x0, double y0, double x1, double y1);
   <span>CanvasGradient</span> <span data-x="dom-context-2d-createRadialGradient">createRadialGradient</span>(double x0, double y0, double r0, double x1, double y1, double r1);
-  <span>CanvasPattern</span> <span data-x="dom-context-2d-createPattern">createPattern</span>(<span>CanvasImageSource</span> image, [TreatNullAs=EmptyString] DOMString repetition);
+  <span>CanvasPattern?</span> <span data-x="dom-context-2d-createPattern">createPattern</span>(<span>CanvasImageSource</span> image, [TreatNullAs=EmptyString] DOMString repetition);
 <!--
   // v8 we received one request from Ralf Richard G&oml;bel for a new kind of pattern: a hatch.
   // basically it would be a series of dash styles, angles, line widths, and offsets
@@ -116696,6 +116696,7 @@ INSERT INTERFACES HERE
   Michael Dyck,
   Michael Enright,
   Michael Gratton,
+  Michael Kohler,
   Michael Nordman,
   Michael Powers,
   Michael Rakowski,