Minor fix for base::Bind documentation

base/callback.h

Index: base/callback.h
diff --git a/base/callback.h b/base/callback.h
index 6a50cbcb7f597278c9bf821ce7a5cd3938be2c4f..eada958591b245463eeb5a59d86f48b3d4a04239 100644
--- a/base/callback.h
+++ b/base/callback.h
@@ -123,7 +123,7 @@
 //   the rest when you execute the callback.
 //
 //   void MyFunc(int i, const std::string& str) {}
-//   base::Callback<void(int)> cb = base::Bind(&MyFunc, 23);
+//   base::Callback<void(const std::string)> cb = base::Bind(&MyFunc, 23);
 //   cb.Run("hello world");
 //
 //   When calling a function bound parameters are first, followed by unbound