Add Get/SetUniqueIdForProcess.

base/process/process_handle.cc

Index: base/process/process_handle.cc
diff --git a/base/process/process_handle.cc b/base/process/process_handle.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3ec91175614cb62fab30f88038dde7059f141615
--- /dev/null
+++ b/base/process/process_handle.cc
@@ -0,0 +1,39 @@
+// Copyright 2015 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/basictypes.h"
+#include "base/logging.h"
+#include "base/process/process_handle.h"
+
+namespace base {
+
+namespace {
+uint32 g_unique_id = kInvalidUniqueId;
+
+#if DCHECK_IS_ON()
+// The process which set g_unique_id.

[Lei Zhang, 2015/07/28 21:54:23]

Please refer to variables are |foo|. Ditto below.

[rickyz (no longer on Chrome), 2015/07/28 22:39:37]

Done.

+uint32 g_procid;
+#endif
+}  // namespace
+
+uint32 GetUniqueIdForProcess() {
+  if (g_unique_id == kInvalidUniqueId) {
+    return static_cast<uint32>(GetCurrentProcId());
+  }
+
+  // Make sure we are the same process that set g_procid. This check may have
+  // false negatives (if a process ID was reused) but should have no false
+  // positives.
+  DCHECK_EQ(static_cast<uint32>(GetCurrentProcId()), g_procid);
+  return g_unique_id;
+}
+
+void SetUniqueIdForProcess(uint32 unique_id) {
+  g_unique_id = unique_id;
+#if DCHECK_IS_ON()
+  g_procid = static_cast<uint32>(GetCurrentProcId());
+#endif
+}
+
+}  // namespace base