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..b3e296f5355c423d6468e06d3c8683722a8872c5 100644
--- a/base/process/process_handle.h
+++ b/base/process/process_handle.h
@@ -34,9 +34,24 @@ 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 globally unique ID for the current process. This defaults to the

[mdempsky, 2015/06/15 21:53:09]

I think "globally" might be misinterpretable.  It might be better to clarify
that the ID is unique across all live processes within the chrome session.  (I
don't think we're making a stronger guarantee than that?  I.e., other chrome
sessions can in the future reuse IDs, and if a process exits its ID can be
reused.)

[rickyz (no longer on Chrome), 2015/06/15 22:09:47]

Ah, good point, changed.

+// process process ID, but may return a different value if SetUniqueIdForProcess

[mdempsky, 2015/06/15 21:53:09]

Should "process process ID" be "process's process ID"?

[rickyz (no longer on Chrome), 2015/06/15 22:09:46]

Done.

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