Move base::FreeDeleter into its own header.

base/memory/free_deleter.h

+// Copyright 2016 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 BASE_MEMORY_FREE_DELETER_H_
+#define BASE_MEMORY_FREE_DELETER_H_
+
+#include <stdlib.h>
+
+namespace base {
+
+// Function object which invokes 'free' on its parameter, which must be
+// a pointer. Can be used to store malloc-allocated pointers in std::unique_ptr:
+//
+// std::unique_ptr<int, base::FreeDeleter> foo_ptr(
+//     static_cast<int*>(malloc(sizeof(int))));
+struct FreeDeleter {
+  inline void operator()(void* ptr) const {
+    free(ptr);
+  }
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_FREE_DELETER_H_