Make [TreatNullAs=NullString] DOMString arguments nullable instead

Source/core/html/canvas/CanvasRenderingContext2D.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 53 matching lines @@
     // image smoothing
     [ImplementedAs=imageSmoothingEnabled, MeasureAs=PrefixedImageSmoothingEnabled] attribute boolean webkitImageSmoothingEnabled;
     [MeasureAs=UnprefixedImageSmoothingEnabled] attribute boolean imageSmoothingEnabled;
 
     // colors and styles (see also the CanvasDrawingStyles interface)
     // FIXME: Use union types when supported: http://crbug.com/372891
     [Custom] attribute object strokeStyle; // (default black)
     [Custom] attribute object fillStyle; // (default black)
     CanvasGradient createLinearGradient(float x0, float y0, float x1, float y1);
     [RaisesException] CanvasGradient createRadialGradient(float x0, float y0, float r0, float x1, float y1, float r1);
-    [RaisesException] CanvasPattern createPattern(HTMLCanvasElement canvas, [TreatNullAs=NullString] DOMString repetitionType);
-    [RaisesException] CanvasPattern createPattern(HTMLImageElement image, [TreatNullAs=NullString] DOMString repetitionType);
-    [RaisesException] CanvasPattern createPattern(HTMLVideoElement image, [TreatNullAs=NullString] DOMString repetitionType);
+    [RaisesException] CanvasPattern createPattern(HTMLCanvasElement canvas, DOMString? repetitionType);
+    [RaisesException] CanvasPattern createPattern(HTMLImageElement image, DOMString? repetitionType);
+    [RaisesException] CanvasPattern createPattern(HTMLVideoElement image, DOMString? repetitionType);
 
     // shadows
     attribute unrestricted float shadowOffsetX;
     attribute unrestricted float shadowOffsetY;
     attribute unrestricted float shadowBlur;
     [TreatNullAs=NullString] attribute DOMString shadowColor;
 
     // rects
     void clearRect(unrestricted float x, unrestricted float y, unrestricted float width, unrestricted float height);
     void fillRect(unrestricted float x, unrestricted float y, unrestricted float width, unrestricted float height);
@@ skipping 93 matching lines @@
     [MeasureAs=CanvasRenderingContext2DDrawImageFromRect] void drawImageFromRect(
         HTMLImageElement? image, optional unrestricted float sx, optional unrestricted float sy, optional unrestricted float sw, optional unrestricted float sh,
         optional unrestricted float dx, optional unrestricted float dy, optional unrestricted float dw, optional unrestricted float dh, optional DOMString compositeOperation);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, optional DOMString color, optional unrestricted float alpha);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float grayLevel, optional unrestricted float alpha);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float r, unrestricted float g, unrestricted float b, unrestricted float a);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float c, unrestricted float m, unrestricted float y, unrestricted float k, unrestricted float a);
 };
 
 CanvasRenderingContext2D implements CanvasPathMethods;