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

chrome/browser/push_messaging/background_budget_service.h

Index: chrome/browser/push_messaging/background_budget_service.h
diff --git a/chrome/browser/push_messaging/background_budget_service.h b/chrome/browser/push_messaging/background_budget_service.h
index 717545a02a6ac464045d7268f625bd42b39610d2..7d3cc28073a6c0b450cfb382230d02cafa205631 100644
--- a/chrome/browser/push_messaging/background_budget_service.h
+++ b/chrome/browser/push_messaging/background_budget_service.h
@@ -33,6 +33,16 @@ class BackgroundBudgetService : public KeyedService {
 
   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.
@@ -51,6 +61,9 @@ class BackgroundBudgetService : public KeyedService {
   // 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);
 };