Support currentTransform in 2D Canvas.

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 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 enum CanvasWindingRule { "nonzero", "evenodd" };
 
 interface CanvasRenderingContext2D : CanvasRenderingContext {
 
     void save();
     void restore();
 
+    [EnabledAtRuntime=ExperimentalCanvasFeatures, Immutable] attribute SVGMatrix currentTransform;
     void scale(float sx, float sy);
     void rotate(float angle);
     void translate(float tx, float ty);
     void transform(float m11, float m12, float m21, float m22, float dx, float dy);
     void setTransform(float m11, float m12, float m21, float m22, float dx, float dy);
     void resetTransform();
 
     attribute float globalAlpha;
     [TreatNullAs=NullString] attribute DOMString globalCompositeOperation;
 
@@ skipping 123 matching lines @@
     [EnabledAtRuntime=ExperimentalCanvasFeatures] boolean drawCustomFocusRing(Element element);
 
     readonly attribute float webkitBackingStorePixelRatio;
 
     [ImplementedAs=imageSmoothingEnabled] attribute boolean webkitImageSmoothingEnabled;
     attribute boolean imageSmoothingEnabled;
 
     Canvas2DContextAttributes getContextAttributes();
 };