Extend base::Callback to have a move-only variant

base/callback_unittest.nc

 // Copyright (c) 2011 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.
 
 // This is a "No Compile Test" suite.
 // http://dev.chromium.org/developers/testing/no-compile-tests
 
 #include "base/callback.h"
 
 namespace base {
 
 class Parent {
 };
 
 class Child : Parent {
 };
 
-#if defined(NCTEST_EQUALS_REQUIRES_SAMETYPE)  // [r"fatal error: no viable conversion from 'Callback<int \(\)>' to 'const Callback<void \(\)>'"]
+#if defined(NCTEST_EQUALS_REQUIRES_SAMETYPE)  // [r"fatal error: no viable conversion from 'Callback<int \(\), \[\.\.\.\]>' to 'const Callback<void \(\), \[\.\.\.\]>'"]
 
 // Attempting to call comparison function on two callbacks of different type.
 //
 // This should be a compile time failure because each callback type should be
 // considered distinct.
 void WontCompile() {
   Closure c1;
   Callback<int()> c2;
   c1.Equals(c2);
 }
@@ skipping 15 matching lines @@
 // See explanation for NCTEST_CONSTRUCTION_FROM_SUBTYPE
 void WontCompile() {
   Callback<Parent()> cb_a;
   Callback<Child()> cb_b;
   cb_a = cb_b;
 }
 
 #endif
 
 }  // namespace base