Fix midnight determination

components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc

 // Copyright 2014 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 "components/data_reduction_proxy/browser/data_reduction_proxy_metrics.h"
 
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 378 matching lines @@
   const int kMaxDaysSinceUnixEpoch = 365 * 1000;  // 1000 years.
   if (time_since_unix_epoch.InDays() < kMinDaysSinceUnixEpoch ||
       time_since_unix_epoch.InDays() > kMaxDaysSinceUnixEpoch) {
     return;
   }
 
   // Determine how many days it has been since the last update.
   int64 then_internal = prefs->GetInt64(
       data_reduction_proxy::prefs::kDailyHttpContentLengthLastUpdateDate);
 
-#if defined(OS_WIN)
-  base::Time then_midnight = base::Time::FromInternalValue(then_internal);
-  base::Time midnight =
-      base::Time::FromInternalValue(
-          (now.ToInternalValue() / base::Time::kMicrosecondsPerDay) *
-              base::Time::kMicrosecondsPerDay);
-#else
   // Local midnight could have been shifted due to time zone change.
-  base::Time then_midnight =
-      base::Time::FromInternalValue(then_internal).LocalMidnight();
+  // If time is null then don't care if midnight will be wrong shifted due to
+  // time zone change because it's still too much time ago.
+  base::Time then_midnight;
+  if (then_internal != 0) {

[bengr, 2014/08/25 21:37:08]

nit: We shouldn't use or assume anything about the internal representation of
time. So perhaps do:

base::Time then_midnight = 
    base::Time::FromInternalValue(then_internal);
if (then_midnight != base::Time())
  then_midnight = then_midnight.LocalMidnight();

+    then_midnight =
+        base::Time::FromInternalValue(then_internal).LocalMidnight();
+  }
   base::Time midnight = now.LocalMidnight();
-#endif
 
   int days_since_last_update = (midnight - then_midnight).InDays();
 
   // Each day, we calculate the total number of bytes received and the total
   // size of all corresponding resources before any data-reducing recompression
   // is applied. These values are used to compute the data savings realized
   // by applying our compression techniques. Totals for the last
   // |kNumDaysInHistory| days are maintained.
   DailyDataSavingUpdate total(
       data_reduction_proxy::prefs::kDailyHttpOriginalContentLength,
@@ skipping 113 matching lines @@
   UpdateContentLengthPrefsForDataReductionProxy(
       received_content_length,
       original_content_length,
       with_data_reduction_proxy_enabled,
       request_type,
       base::Time::Now(),
       prefs);
 }
 
 }  // namespace data_reduction_proxy