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

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 3b0b4b595c240e49c2e02e834c2d66e5a0b24105..1669b06bc7237563637685e1667c0971fce9d328 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -42701,6 +42701,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PushMessaging.BackgroundBudget">
+  <owner>harkness@chromium.org</owner>
+  <summary>
+    Whenever a Service Worker receives a push message, this records the budget
+    available to the service worker, which is an internal Chrome value for the
+    amount of background processing a service worker is allowed to do without
+    visibly alerting the user. Scale for the budget is 0 to 100.
+  </summary>
+</histogram>
+
 <histogram name="PushMessaging.DeliveryStatus" enum="PushDeliveryStatus">
   <owner>johnme@google.com</owner>
   <owner>mvanouwerkerk@google.com</owner>
@@ -42731,6 +42741,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PushMessaging.SESForLowBudgetOrigin">
+  <owner>harkness@chromium.org</owner>
+  <summary>
+    When a Service Worker hits low budget when servicing a push message, this
+    records what the Site Engagement Service score is at that time.
+  </summary>
+</histogram>
+
+<histogram name="PushMessaging.SESForNoBudgetOrigin">
+  <owner>harkness@chromium.org</owner>
+  <summary>
+    When a Service Worker hits zero budget when servicing a push message, this
+    records what the Site Engagement Service score is at that time.
+  </summary>
+</histogram>
+
 <histogram name="PushMessaging.UnregistrationStatus"
     enum="PushUnregistrationStatus">
   <owner>johnme@google.com</owner>