Added UMA stats to track the budget for any service worker which receives a

chrome/browser/push_messaging/background_budget_service.h

 // 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.
 
 #ifndef CHROME_BROWSER_PUSH_MESSAGING_BACKGROUND_BUDGET_SERVICE_H_
 #define CHROME_BROWSER_PUSH_MESSAGING_BACKGROUND_BUDGET_SERVICE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 15 matching lines @@
 // worker should be able to do on behalf of the user. The budget is calculated
 // based on the Site Engagment Score and is consumed when a service worker does
 // background work on behalf of the user.
 class BackgroundBudgetService : public KeyedService {
  public:
   explicit BackgroundBudgetService(Profile* profile);
   ~BackgroundBudgetService() override;
 
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
+  enum CostType {

[Peter Beverloo, 2016/05/17 13:51:02]

nit: enum class

[harkness, 2016/05/17 15:49:32]

Done.

+    // The cost of silencing a push message.
+    SILENT_PUSH_COST = 0,
+
+    MAX_COST_TYPE
+  };
+
+  // Query for the base cost for any background processing.
+  static double GetBackgroundProcessingCost(CostType type);
+
   // Get the budget associated with the origin. This is returned as the double
   // budget. Budget will be a value between 0.0 and
   // SiteEngagementScore::kMaxPoints.
   double GetBudget(const GURL& origin);
 
   // Store the budget associated with the origin. Budget should be a value
   // between 0.0 and SiteEngagementScore::kMaxPoints.
   void StoreBudget(const GURL& origin, double budget);
 
  private:
   friend class BackgroundBudgetServiceTest;
 
   // Used to allow tests to fast forward/reverse time.
   void SetClockForTesting(std::unique_ptr<base::Clock> clock);
 
   // The clock used to vend times.
   std::unique_ptr<base::Clock> clock_;
 
+  // Array holding the costs for various background operations.
+  static double costs_[];

[Peter Beverloo, 2016/05/17 13:51:01]

This can live in an anonymous namespace, no need to expose it in the interface.

In general, it would be cleaner to just have an switch() case in
GetBackgroundProcessingCost, that can immediately give us compile-time
verification that we didn't accidentally forget about adding a value when
introducing a new cost, if you omit the default case.

[harkness, 2016/05/17 15:49:32]

As discussed in person, I'm just returning the result values from GetCost,
rather than defining a constant value and then returning that.

+
   Profile* profile_;
   DISALLOW_COPY_AND_ASSIGN(BackgroundBudgetService);
 };
 
 #endif  // CHROME_BROWSER_PUSH_MESSAGING_BACKGROUND_BUDGET_SERVICE_H_