IDL: Don't lose nullable flag when "preprocessing" type

Source/core/html/canvas/WebGLRenderingContextBase.idl

 /*
  * Copyright (C) 2009 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 538 matching lines @@
     sequence<WebGLShader>? getAttachedShaders(WebGLProgram? program);
 
     GLint getAttribLocation(WebGLProgram? program, DOMString name);
 
     [CallWith=ScriptState] any getBufferParameter(GLenum target, GLenum pname);
 
     WebGLContextAttributes? getContextAttributes();
 
     GLenum getError();
 
-    object? getExtension(DOMString name);
+    [CallWith=ScriptState] object? getExtension(DOMString name);
 
     [CallWith=ScriptState] any getFramebufferAttachmentParameter(GLenum target, GLenum attachment, GLenum pname);
     [CallWith=ScriptState] any getParameter(GLenum pname);
     [CallWith=ScriptState] any getProgramParameter(WebGLProgram? program, GLenum pname);
     DOMString? getProgramInfoLog(WebGLProgram? program);
     [CallWith=ScriptState] any getRenderbufferParameter(GLenum target, GLenum pname);
     [CallWith=ScriptState] any getShaderParameter(WebGLShader? shader, GLenum pname);
 
     DOMString?   getShaderInfoLog(WebGLShader? shader);
 
@@ skipping 125 matching lines @@
     void vertexAttrib3fv(GLuint indx, Float32Array values);
     void vertexAttrib3fv(GLuint indx, sequence<GLfloat> values);
     void vertexAttrib4f(GLuint indx, GLfloat x, GLfloat y, GLfloat z, GLfloat w);
     void vertexAttrib4fv(GLuint indx, Float32Array values);
     void vertexAttrib4fv(GLuint indx, sequence<GLfloat> values);
     void vertexAttribPointer(GLuint indx, GLint size, GLenum type, GLboolean normalized,
                              GLsizei stride, GLintptr offset);
 
     void viewport(GLint x, GLint y, GLsizei width, GLsizei height);
 };