Give access to a network time kept in the variation service.

chrome/browser/metrics/variations/network_time_tracker_unittest.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/threading/platform_thread.h"
+#include "chrome/browser/metrics/variations/network_time_tracker.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+// These are all in milliseconds.
+const int64 kLatency1 = 50;
+const int64 kLatency2 = 500;
+
+// Can not be smaller than 15, it's the NowFromSystemTime() resolution.
+const int64 kResolution1 = 17;
+const int64 kResolution2 = 177;
+
+const int64 kSleepTime1 = 500;
+const int64 kSleepTime2 = 333;
+
+void ValidateCurrentTime(const NetworkTimeTracker& network_time_tracker) {
+  base::Time expected_time = base::Time::NowFromSystemTime();
+  base::Time network_time;
+  base::TimeDelta uncertainty;
+  EXPECT_TRUE(network_time_tracker.GetNetworkTime(&network_time,
+                                                  &uncertainty));
+  EXPECT_LE(abs(expected_time.ToInternalValue() -
+                network_time.ToInternalValue()), uncertainty.ToInternalValue());
+}
+
+}

[Alexei Svitkine (slow), 2013/02/04 21:23:18]

Nit: Add "// namespace".

[MAD, 2013/02/05 01:05:55]

Done.

+
+TEST(NetworkTimeTrackerTest, ProperTimeTracking) {
+  NetworkTimeTracker network_time_tracker;
+
+  // Should not return a value before UpdateNetworkTime gets called.
+  base::Time network_time;
+  base::TimeDelta uncertainty;
+  EXPECT_FALSE(network_time_tracker.GetNetworkTime(&network_time,
+                                                   &uncertainty));
+
+  // Update the time based on NowFromSystemTime and kLatency1.
+  network_time_tracker.UpdateNetworkTime(
+      base::Time::NowFromSystemTime(),
+      base::TimeDelta::FromMilliseconds(kResolution1),
+      base::TimeDelta::FromMilliseconds(kLatency1));
+  ValidateCurrentTime(network_time_tracker);
+
+  // Wait for kSleepTime1 to make sure we keep tracking.
+  base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(kSleepTime1));

[Alexei Svitkine (slow), 2013/02/04 21:23:18]

Instead of making the test sleep (which makes the test slow and bad for cycle
times, etc), how about mocking out base::TimeTicks::Now().

If there's no facility to do that already globally, just add a GetCurrentTime()
virtual method to the class and override it in the test.

Alternatively, you can add it as a parameter to the function APIs. Then, you can
make VariationsService pass base::Time::Now() to them, so that users getting the
time via VariationsService don't have to deal with it.

[MAD, 2013/02/05 01:05:55]

Done.

+  ValidateCurrentTime(network_time_tracker);
+
+  // Update the time with a new NowFromSystemTime value and kLatency2.
+  network_time_tracker.UpdateNetworkTime(
+      base::Time::NowFromSystemTime(),
+      base::TimeDelta::FromMilliseconds(kResolution2),
+      base::TimeDelta::FromMilliseconds(kLatency2));
+
+  // Wait for kSleepTime2 to make sure we keep tracking still.
+  base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(kSleepTime2));
+  ValidateCurrentTime(network_time_tracker);
+}