Add support for nullable operation arguments in IDL files

Source/bindings/tests/idls/TestObject.idl

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary formstrArg, 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.
@@ skipping 247 matching lines @@
 
     void variadicStringMethod(DOMString head, DOMString... tail);
     void variadicDoubleMethod(double head, double... tail);
     void variadicNodeMethod(Node head, Node... tail);
 
     // Nullable attributes.
     readonly attribute double? nullableDoubleAttribute;
     readonly attribute long? nullableLongAttribute;
     readonly attribute boolean? nullableBooleanAttribute;
     readonly attribute DOMString? nullableStringAttribute;
+    attribute long? nullableLongSettableAttribute;
+    [GetterRaisesException] attribute long? nullableStringValue;
 
-    attribute long? nullableLongSettableAttribute;
-
-    [GetterRaisesException] attribute long? nullableStringValue;
+    // Nullable arguments.
+    void methodWithNullableArguments(DOMString? str, long? l, TestObject? obj, optional double? d);
 
     [PerWorldBindings] readonly attribute TestObject perWorldReadOnlyAttribute;
     [PerWorldBindings] attribute TestObject perWorldAttribute;
     [PerWorldBindings] void perWorldMethod();
     [PerWorldBindings] void overloadedPerWorldMethod(long longArg);
     [PerWorldBindings] void overloadedPerWorldMethod(DOMString strArg, long longArg);
 
     [ActivityLogging=Access] void activityLoggedMethod1(long longArg);
     [PerWorldBindings, ActivityLogging=Access] void activityLoggedMethod2(long longArg);
     [PerWorldBindings, ActivityLogging=AccessForIsolatedWorlds] void activityLoggedInIsolatedWorldMethod(long longArg);
@@ skipping 17 matching lines @@
 
     [DeprecateAs=Method] void deprecatedMethod();
     [DeprecateAs=StaticMethod] static void deprecatedStaticMethod();
 
     [DeprecateAs=Constant] const unsigned short DEPRECATED_CONSTANT = 1;
 };
 
 // The following comment should not generate any code
 // TestObject implements TestImplements;