Move global_descriptors to base/posix.

base/global_descriptors_posix.h

-// Copyright (c) 2012 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_GLOBAL_DESCRIPTORS_POSIX_H_
-#define BASE_GLOBAL_DESCRIPTORS_POSIX_H_
-
-#include "build/build_config.h"
-
-#include <vector>
-#include <utility>
-
-#include <stdint.h>
-
-#include "base/memory/singleton.h"
-
-namespace base {
-
-// It's common practice to install file descriptors into well known slot
-// numbers before execing a child; stdin, stdout and stderr are ubiqutous
-// examples.
-//
-// However, when using a zygote model, this becomes troublesome. Since the
-// descriptors which need to be in these slots generally aren't known, any code
-// could open a resource and take one of the reserved descriptors. Simply
-// overwriting the slot isn't a viable solution.
-//
-// We could try to fill the reserved slots as soon as possible, but this is a
-// fragile solution since global constructors etc are able to open files.
-//
-// Instead, we retreat from the idea of installing descriptors in specific
-// slots and add a layer of indirection in the form of this singleton object.
-// It maps from an abstract key to a descriptor. If independent modules each
-// need to define keys, then values should be chosen randomly so as not to
-// collide.
-class BASE_EXPORT GlobalDescriptors {
- public:
-  typedef uint32_t Key;
-  typedef std::pair<Key, int> KeyFDPair;
-  typedef std::vector<KeyFDPair> Mapping;
-
-  // Often we want a canonical descriptor for a given Key. In this case, we add
-  // the following constant to the key value:
-  static const int kBaseDescriptor = 3;  // 0, 1, 2 are already taken.
-
-  // Return the singleton instance of GlobalDescriptors.
-  static GlobalDescriptors* GetInstance();
-
-  // Get a descriptor given a key. It is a fatal error if the key is not known.
-  int Get(Key key) const;
-
-  // Get a descriptor give a key. Returns -1 on error.
-  int MaybeGet(Key key) const;
-
-  // Set the descriptor for the given key.
-  void Set(Key key, int fd);
-
-  void Reset(const Mapping& mapping);
-
- private:
-  friend struct DefaultSingletonTraits<GlobalDescriptors>;
-  GlobalDescriptors();
-  ~GlobalDescriptors();
-
-  Mapping descriptors_;
-};
-
-}  // namespace base
-
-#endif  // BASE_GLOBAL_DESCRIPTORS_POSIX_H_