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..17a95835302470475e4d3c23a00be82d5e84851e 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 +97,15 @@ void BackgroundBudgetService::RegisterProfilePrefs(
   registry->RegisterDictionaryPref(prefs::kBackgroundBudgetMap);
 }
 
+double BackgroundBudgetService::costs_[] = {
+    2.0,  // SILENT_PUSH_COST
+};
+
+// static
+double BackgroundBudgetService::GetBackgroundProcessingCost(CostType type) {
+  return costs_[type];
+}
+
 double BackgroundBudgetService::GetBudget(const GURL& origin) {
   DCHECK_EQ(origin, origin.GetOrigin());
 
@@ -136,6 +147,15 @@ 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);
+
+  // Generate histograms for the GetBudget calls which would return "no budget"
+  // or "low budget" if an API was available to app developers.
+  double cost = GetBackgroundProcessingCost(SILENT_PUSH_COST);
+  if (budget < cost)
+    UMA_HISTOGRAM_COUNTS("PushMessaging.SESForNoBudgetOrigin", ses_score);
+  else if (budget < 2.0 * cost)
+    UMA_HISTOGRAM_COUNTS("PushMessaging.SESForLowBudgetOrigin", ses_score);

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

To this and the other histograms:

UMA_HISTOGRAM_COUNTS counts 50 buckets in a range of 1 to 1,000,000. We know
|budget| to be in range of [0, 100], so please use UMA_HISTOGRAM_COUNTS_100
instead. That macro counts 50 buckets in a range of 1 to a hundred.

Since buckets have higher granularity for the lower counts, I also wonder what
we gain by having three separate histograms. (I know we discussed this in the
past, but I forgot— sorry!)

We know that-
  (1) PushMessaging.BackgroundBudget will record budgets in the range of [0,
100].
  (2) PushMessaging.SESForNoBudgetOrigin will record budgets in the range of [0,
1.99].
  (3) PushMessaging.SESForLowBudgetOrigin will record budgets in the range of
[2, 3.99].

In addition, lines 151-157 effectively are a layering violation, because it
makes the assumption that budget is being received for push messaging.

Would it make sense to only keep (1)? Michael knows the mechanics of UMA better
than I do.

[Peter Beverloo, 2016/05/17 14:03:23]

Scratch this part, sorry! You're recording the *SES*, not the budget, I need to
read better :).

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

I updated to UMA_HISTOGRAM_COUNTS_100 for all three and moved the SES related
ones into push_messaging_notification_manager.cc

+
   return budget;
 }