Have bindings layer assume and insist that all interface types are GCed.

third_party/WebKit/Source/modules/canvas2d/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 18 matching lines @@
          HTMLVideoElement or
          HTMLCanvasElement or
          // CanvasRenderingContext2D or
          ImageBitmap) CanvasImageSource;
 
 enum CanvasFillRule { "nonzero", "evenodd" };
 enum ImageSmoothingQuality {"low", "medium", "high"};
 
 [
     SetWrapperReferenceFrom=canvas,
-    GarbageCollected,
 ] interface CanvasRenderingContext2D {
     // back-reference to the canvas
     readonly attribute HTMLCanvasElement canvas;
 
     // state
     void save(); // push state on state stack
     void restore(); // pop state stack and restore state
 
     // transformations (default transform is the identity matrix)
     [RuntimeEnabled=ExperimentalCanvasFeatures] attribute SVGMatrix currentTransform;
@@ skipping 92 matching lines @@
 
     // text
     attribute DOMString font; // (default 10px sans-serif)
     attribute DOMString textAlign; // "start", "end", "left", "right", "center" (default: "start")
     attribute DOMString textBaseline; // "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" (default: "alphabetic")
     [RuntimeEnabled=ExperimentalCanvasFeatures] attribute DOMString direction; // "inherit", "rtl", "ltr" (default: "inherit")
 
 };
 
 CanvasRenderingContext2D implements CanvasPathMethods;