Allow MakeCriticalClosure to enclose closures with non-void return types.

base/critical_closure_internal_ios.mm

Index: base/critical_closure_internal_ios.mm
diff --git a/base/critical_closure_internal_ios.mm b/base/critical_closure_internal_ios.mm
new file mode 100644
index 0000000000000000000000000000000000000000..b8fec141b2198e53c2b8e2d4826a1fba7edc0212
--- /dev/null
+++ b/base/critical_closure_internal_ios.mm
@@ -0,0 +1,17 @@
+// 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.
+
+#include "base/critical_closure.h"
+
+#import <UIKit/UIKit.h>
+
+namespace base {
+namespace internal {
+
+bool IsMultiTaskingSupported() {
+  return [[UIDevice currentDevice] isMultitaskingSupported];
+}
+
+}  // namespace internal
+}  // namespace base