Added code to make sure that the budget service does sane things if the clock rolls backwards.

chrome/browser/push_messaging/background_budget_service.cc

 // Copyright 2016 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/push_messaging/background_budget_service.h"
 
 #include <stdint.h>
 
 #include "base/callback.h"
 #include "base/memory/ptr_util.h"
@@ skipping 111 matching lines @@
   if (!GetBudgetDataFromPrefs(profile_, origin, &old_budget, &old_ses,
                               &last_updated_msec)) {
     // If there is no stored data or the data can't be parsed, just return the
     // SES.
     return ses_score;
   }
 
   base::Time now = clock_->Now();
   base::TimeDelta elapsed = now - base::Time::FromDoubleT(last_updated_msec);
 
+  // The user can set their clock backwards, so if the last updated time is in
+  // the future, don't update the budget based on elapsed time. Eventually the
+  // clock will reach the future, and the budget calculations will catch up.
+  // TODO(harkness): Consider what to do if the clock jumps forward by a
+  // significant amount.
+  if (elapsed.InMicroseconds() < 0)
+    return old_budget;
+
   // For each time period that elapses, calculate the carryover ratio as the
   // ratio of time remaining in our max period to the total period.
   // The carryover component is then the old budget multiplied by the ratio.
   double carryover_ratio = std::max(
       0.0,
       ((kSecondsToAccumulate - elapsed.InSeconds()) / kSecondsToAccumulate));
   double budget_carryover = old_budget * carryover_ratio;
 
   // The ses component is an average of the last ses score used for budget
   // calculation and the current ses score.
@@ skipping 23 matching lines @@
 
   base::Time time = clock_->Now();
   SetBudgetDataInPrefs(profile_, origin, time.ToDoubleT(), budget, ses_score);
 }
 
 // Override the default clock with the specified clock. Only used for testing.
 void BackgroundBudgetService::SetClockForTesting(
     std::unique_ptr<base::Clock> clock) {
   clock_ = std::move(clock);
 }