Add Get/SetUniqueIdForProcess.

base/process/process_handle.h

 // Copyright (c) 2013 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_PROCESS_PROCESS_HANDLE_H_
 #define BASE_PROCESS_PROCESS_HANDLE_H_
 
+#include <stdint.h>
+#include <sys/types.h>
+
 #include "base/base_export.h"
-#include "base/basictypes.h"
 #include "base/files/file_path.h"
 #include "build/build_config.h"
 
-#include <sys/types.h>
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
 
 namespace base {
 
 // ProcessHandle is a platform specific type which represents the underlying OS
 // handle to a process.
 // ProcessId is a number which identifies the process in the OS.
 #if defined(OS_WIN)
 typedef HANDLE ProcessHandle;
 typedef DWORD ProcessId;
 typedef HANDLE UserTokenHandle;
 const ProcessHandle kNullProcessHandle = NULL;
 const ProcessId kNullProcessId = 0;
 #elif defined(OS_POSIX)
 // On POSIX, our ProcessHandle will just be the PID.
 typedef pid_t ProcessHandle;
 typedef pid_t ProcessId;
 const ProcessHandle kNullProcessHandle = 0;
 const ProcessId kNullProcessId = 0;
 #endif  // defined(OS_WIN)
 
 // Returns the id of the current process.
+// Note that on some platforms, this is not guaranteed to be unique across
+// processes (use GetUniqueIdForProcess if uniqueness is required).
 BASE_EXPORT ProcessId GetCurrentProcId();
 
+// Returns a unique ID for the current process. The ID will be unique across all
+// currently running processes within the chrome session, but IDs of terminated
+// processes may be reused. This returns an opaque value that is different from
+// a process's PID.
+BASE_EXPORT uint32_t GetUniqueIdForProcess();
+
+#if defined(OS_LINUX)
+// When a process is started in a different PID namespace from the browser
+// process, this function must be called with the process's PID in the browser's
+// PID namespace in order to initialize its unique ID. Not thread safe.
+// WARNING: To avoid inconsistent results from GetUniqueIdForProcess, this
+// should only be called very early after process startup - ideally as soon
+// after process creation as possible.
+BASE_EXPORT void InitUniqueIdForProcessInPidNamespace(
+    ProcessId pid_outside_of_namespace);
+#endif
+
 // Returns the ProcessHandle of the current process.
 BASE_EXPORT ProcessHandle GetCurrentProcessHandle();
 
-// Returns the unique ID for the specified process. This is functionally the
-// same as Windows' GetProcessId(), but works on versions of Windows before
-// Win XP SP1 as well.
+// Returns the process ID for the specified process. This is functionally the
+// same as Windows' GetProcessId(), but works on versions of Windows before Win
+// XP SP1 as well.
 // DEPRECATED. New code should be using Process::Pid() instead.
+// Note that on some platforms, this is not guaranteed to be unique across
+// processes.
 BASE_EXPORT ProcessId GetProcId(ProcessHandle process);
 
 #if defined(OS_POSIX)
 // Returns the path to the executable of the given process.
 BASE_EXPORT FilePath GetProcessExecutablePath(ProcessHandle process);
 
 // Returns the ID for the parent of the given process.
 BASE_EXPORT ProcessId GetParentProcessId(ProcessHandle process);
 #endif
 
 }  // namespace base
 
 #endif  // BASE_PROCESS_PROCESS_HANDLE_H_