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

third_party/WebKit/Source/core/css/WebKitCSSMatrix.idl

 /*
  * Copyright (C) 2008, 2010 Apple 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 11 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // Introduced in DOM Level ?:
 [
     Constructor(optional DOMString cssValue = null),
     ConstructorCallWith=ExecutionContext,
     ImplementedAs=CSSMatrix,
     RaisesException=Constructor,
-    GarbageCollected
 ] interface WebKitCSSMatrix {
 
     // These attributes are simple aliases for certain elements of the 4x4 matrix
     attribute unrestricted double a; // alias for m11
     attribute unrestricted double b; // alias for m12
     attribute unrestricted double c; // alias for m21
     attribute unrestricted double d; // alias for m22
     attribute unrestricted double e; // alias for m41
     attribute unrestricted double f; // alias for m42
 
@@ skipping 53 matching lines @@
     // Returns this matrix skewed along the X axis by the passed values.
     // Passing a NaN will use a value of 0.
     WebKitCSSMatrix skewX([Default=Undefined] optional unrestricted double angle);
 
     // Returns this matrix skewed along the Y axis by the passed values.
     // Passing a NaN will use a value of 0.
     WebKitCSSMatrix skewY([Default=Undefined] optional unrestricted double angle);
 
     [NotEnumerable] stringifier;
 };