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

chrome/browser/push_messaging/background_budget_service.cc

Index: chrome/browser/push_messaging/background_budget_service.cc
diff --git a/chrome/browser/push_messaging/background_budget_service.cc b/chrome/browser/push_messaging/background_budget_service.cc
index 5963bc288873b2ae56b54911f30177f9bb108c42..44d6f6427d2a796a9ab3b56966d84e9b9bf56bb6 100644
--- a/chrome/browser/push_messaging/background_budget_service.cc
+++ b/chrome/browser/push_messaging/background_budget_service.cc
@@ -8,6 +8,7 @@
 
 #include "base/callback.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
@@ -24,7 +25,8 @@
 namespace {
 
 constexpr char kSeparator = '#';
-// We calculate the ratio of the different components of a budget with respect
+
+// Calculate the ratio of the different components of a budget with respect
 // to a maximum time period of 10 days = 864000.0 seconds.
 constexpr double kSecondsToAccumulate = 864000.0;
 
@@ -95,6 +97,16 @@ void BackgroundBudgetService::RegisterProfilePrefs(
   registry->RegisterDictionaryPref(prefs::kBackgroundBudgetMap);
 }
 
+// static
+double BackgroundBudgetService::GetCost(CostType type) {
+  switch (type) {
+    case CostType::SILENT_PUSH:
+      return 2.0;
+      // No default case.

[Peter Beverloo, 2016/05/17 15:54:28]

nit: -2 indent

[harkness, 2016/05/17 16:18:05]

Done.

+  }
+  DCHECK(false);

[Peter Beverloo, 2016/05/17 15:54:28]

Since DCHECKS() are removed from release builds, this will actually cause a
compile failure because there is no return value. What about:

  NOTREACHED();
  return SiteEngagementScore::GetMaxPoints();

[harkness, 2016/05/17 16:18:05]

Done.

+}
+
 double BackgroundBudgetService::GetBudget(const GURL& origin) {
   DCHECK_EQ(origin, origin.GetOrigin());
 
@@ -136,6 +148,7 @@ double BackgroundBudgetService::GetBudget(const GURL& origin) {
   // component, which gives extra budget to sites that have a high ses score.
   double budget = budget_carryover + ses_component;
   DCHECK_GE(budget, 0.0);
+
   return budget;
 }