Replace the 1 in 10 grace period with an accumulating budget based on SES.

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 d9c8411a61c3601664ab44396b45b32654ec744a..78cad2451b8cc285664813db833b03b24302cbbb 100644
--- a/chrome/browser/push_messaging/background_budget_service.h
+++ b/chrome/browser/push_messaging/background_budget_service.h
@@ -7,7 +7,6 @@
 
 #include <string>
 
-#include "base/callback_forward.h"
 #include "url/gurl.h"
 
 class Profile;
@@ -17,24 +16,21 @@ class PrefRegistrySyncable;
 }
 
 // A budget service to help Chrome decide how much background work a service
-// worker should be able to do on behalf of the user. The budget currently
-// implements a grace period of 1 non-visual notification in 10.
+// 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
+// doesn't show a notification when it needed to.
 class BackgroundBudgetService {
  public:
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
-  // Get the budget associated with the origin. This currently tracks a string
-  // which holds 0 and 1 for the last 10 push messages and whether they
-  // triggered a visual notification.
-  static std::string GetBudget(Profile* profile, const GURL& origin);
+  // Get the budget associated with the origin. This is returned as the double
+  // budget.
+  static void GetBudget(Profile* profile, const GURL& origin, double& budget);

[Peter Beverloo, 2016/04/14 18:02:09]

Can we return the double instead? If you do decide to keep it as a parameter,
could you make it a pointer?

While a reference like this technically is allowed nowadays, there is an
important difference in readability. Consider this example:

  {
    double budget = 42.0;
    // ....
    BudgetService::GetBudget(profile, origin, budget);
    // ...
    // What value does |budget| have?
  }

By s/budget/&budget/ is already becomes much more obvious that the variable may
be modified.

[harkness, 2016/04/27 11:21:08]

Done.

 
-  // Store the budget associated with the origin. notifications_shown is
-  // expected to be a string encoding whether the last 10 push messages
-  // triggered
-  // a visual notification.
+  // Store the budget associated with the origin.

[Peter Beverloo, 2016/04/14 18:02:09]

This method, as well as GetBudget(), should document what the expected values of
|budget| are. Can I pass in a budget of 1.798E+308? We should then also have
DCHECKs to make sure the budget stays within that contract.

[harkness, 2016/04/27 11:21:08]

Done. I capped it at 0.0 to the max value of SES. In the future we may consider
going negative on budget, but for now that shouldn't happen.

   static void StoreBudget(Profile* profile,
                           const GURL& origin,
-                          const std::string& notifications_shown);
+                          const double budget);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(BackgroundBudgetService);