Allow implicitly converting a lambda to mojo::Callback using C++11

mojo/public/cpp/bindings/lib/callback_internal.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_
 
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 
 namespace mojo {
 class String;
 
 namespace internal {
 
 template <typename T>
 struct Callback_ParamTraits {
   typedef T ForwardType;
 };
 
 template <>
 struct Callback_ParamTraits<String> {
   typedef const String& ForwardType;
 };
 
-template <typename T, typename... Args>
-struct HasCompatibleCallOperator {
-  // This template's second parameter is the signature of the operator()
-  // overload we want to try to detect:
-  //   void operator()(Args...) const;
-  template <typename U,
-            void (U::*)(
-                typename internal::Callback_ParamTraits<Args>::ForwardType...)
-                const>
-  struct TestType {};
-
-  // This matches type U if it has a call operator with the
-  // expected signature.
-  template <typename U>
-  static YesType Test(TestType<U, &U::operator()>*);
-
-  // This matches anything else.
-  template <typename U>
-  static NoType Test(...);
-
-  // HasCompatibleCallOperator<T, Args...>::value will be true if T has a
-  // compatible call operator.
-  enum { value = (sizeof(Test<T>(nullptr)) == sizeof(YesType)) };
-};
-
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_CALLBACK_INTERNAL_H_