Add Get/SetUniqueIdForProcess.

base/process/process_handle.h

Index: base/process/process_handle.h
diff --git a/base/process/process_handle.h b/base/process/process_handle.h
index 77f2c585cfcc71087596855fa6f83ac643ce9a6c..07bcae01428632e31d8e8709ce7209ba975643a5 100644
--- a/base/process/process_handle.h
+++ b/base/process/process_handle.h
@@ -34,9 +34,26 @@ const ProcessHandle kNullProcessHandle = 0;
 const ProcessId kNullProcessId = 0;
 #endif  // defined(OS_WIN)
 
+// This is not a valid process ID on Linux, Mac, or Windows.
+const uint32 kInvalidUniqueId = 0;
+
 // Returns the id of the current process.
 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 note that IDs of
+// terminated processes may be reused. This defaults to the process's process
+// ID, but may return a different value if SetUniqueIdForProcess has been
+// called.
+BASE_EXPORT uint32 GetUniqueIdForProcess();
+
+// Sets the unique ID for the current process. |unique_id| may not be
+// kInvalidUniqueId.
+// WARNING: To avoid inconsistent results from GetUniqueIdForProcess, this
+// should only be called very early after process startup - ideally as soon
+// after forking as possible.

[jln (very slow on Chromium), 2015/06/15 23:25:08]

s/forking/process creation/ just to be friendly to non-Linux.

[rickyz (no longer on Chrome), 2015/06/17 00:50:33]

Done.

+BASE_EXPORT void SetUniqueIdForProcess(uint32 unique_id);
+
 // Returns the ProcessHandle of the current process.
 BASE_EXPORT ProcessHandle GetCurrentProcessHandle();