Add a new function for getting a deterministic machine ID

chrome/browser/prefs/tracked/device_id_unittest.cc

+// 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 "chrome/browser/prefs/tracked/device_id.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+TEST(GetDeterministicMachineSpecificIdTest, IsDeterministic) {
+  std::string first_machine_id;
+  std::string second_machine_id;
+
+  bool machine_id_enabled = false;
+#if defined(OS_WIN)
+  machine_id_enabled = true;
+#endif

[gab, 2015/01/20 15:34:12]

This will likely change based on other comments, but FTR here's what I had in
mind:

  const bool kMachineIdEnabled =
#if defined(OS_WIN)
      true;
#else
      false;
#endif

[alito, 2015/01/26 16:32:48]

Acknowledged.

+
+  ASSERT_EQ(machine_id_enabled,
+            GetDeterministicMachineSpecificId(&first_machine_id));
+  ASSERT_EQ(machine_id_enabled,
+            GetDeterministicMachineSpecificId(&second_machine_id));
+  if (!machine_id_enabled) {
+    EXPECT_EQ(string(""), first_machine_id);

[gab, 2015/01/20 15:34:12]

I think this test will change based on other comments, but FTR here it's
slightly cleaner to do
EXPECT_TRUE(first_machine_id.empty());

In fact here we also want to make sure it's not empty when one is expected, so
you'd want:

EXPECT_EQ(!kMachineIdEnabled, first_machine_id.empty());

[alito, 2015/01/26 16:32:48]

Acknowledged.

+  }
+  EXPECT_EQ(first_machine_id, second_machine_id);
+}