Support binding WeakPtr<> to methods with void return types.

base/callback.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
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 $var MAX_ARITY = 6
 
 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
@@ skipping 29 matching lines @@
 // and thus do not need to be deleted.
 //
 // The reason to pass via a const-reference is to avoid unnecessary
 // AddRef/Release pairs to the internal state.
 //
 //
 // EXAMPLE USAGE:
 //
 // /* Binding a normal function. */
 // int Return5() { return 5; }
-// base::Callback<int(int)> func_cb = base::Bind(&Return5);
-// LOG(INFO) << func_cb.Run(5);  // Prints 5.
+// base::Callback<int(void)> func_cb = base::Bind(&Return5);
+// LOG(INFO) << func_cb.Run();  // Prints 5.
 //
 // void PrintHi() { LOG(INFO) << "hi."; }
 // base::Closure void_func_cb = base::Bind(&PrintHi);
-// LOG(INFO) << void_func_cb.Run();  // Prints: hi.
+// void_func_cb.Run();  // Prints: hi.
 //
 // /* Binding a class method. */
 // class Ref : public RefCountedThreadSafe<Ref> {
 //  public:
 //   int Foo() { return 3; }
 //   void PrintBye() { LOG(INFO) << "bye."; }
 // };
 // scoped_refptr<Ref> ref = new Ref();
 // base::Callback<int(void)> ref_cb = base::Bind(&Ref::Foo, ref.get());
 // LOG(INFO) << ref_cb.Run();  // Prints out 3.
@@ skipping 118 matching lines @@
 // is not supported by tr1.
 //
 // Lastly, tr1::function and tr1::bind has a more general and flexible API.
 // This includes things like argument reordering by use of
 // tr1::bind::placeholder, support for non-const reference parameters, and some
 // limited amount of subtyping of the tr1::function object (eg.,
 // tr1::function<int(int)> is convertible to tr1::function<void(int)>).
 //
 // These are not features that are required in Chromium. Some of them, such as
 // allowing for reference parameters, and subtyping of functions, may actually
-// because a source of errors. Removing support for these features actually
+// become a source of errors. Removing support for these features actually
 // allows for a simpler implementation, and a terser Currying API.
 //
 //
 // WHY NOT GOOGLE CALLBACKS?
 //
 // The Google callback system also does not support refcounting.  Furthermore,
 // its implementation has a number of strange edge cases with respect to type
 // conversion of its arguments.  In particular, the argument's constness must
 // at times match exactly the function signature, or the type-inference might
 // break.  Given the above, writing a custom solution was easier.
@@ skipping 70 matching lines @@
 
 ]]  $$ for ARITY
 
 // Syntactic sugar to make Callbacks<void(void)> easier to declare since it
 // will be used in a lot of APIs with delayed execution.
 typedef Callback<void(void)> Closure;
 
 }  // namespace base
 
 #endif  // BASE_CALLBACK_H