Add Get/SetUniqueIdForProcess.

base/process/process_handle.cc

+// 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.
+
+#include "base/process/process_handle.h"
+
+namespace base {
+
+namespace {
+uint32 g_unique_id = kInvalidUniqueId;
+}  // namespace
+
+uint32 GetUniqueIdForProcess() {
+  if (g_unique_id == kInvalidUniqueId) {
+    return static_cast<uint32>(GetCurrentProcId());
+  }
+
+  return g_unique_id;
+}
+
+void SetUniqueIdForProcess(uint32 unique_id) {
+  g_unique_id = unique_id;

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

This is not thread_safe. How about using a lazy instance which deals with that
for you?

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

Does it suffice to just document that it is not thread safe? It doesn't make
sense to call this function from multiple threads anyway.

+}
+
+}  // namespace base