Added UMA for usage of BudgetAPI calls.

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 1043e5631c3993d0e32a18ba3388cdb14f3014aa..97a4d4459c00dc8562c279a3e4c57ad8ca496296 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3995,6 +3995,28 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Time spent initializing WindowProxy during a page loading.</summary>
 </histogram>
 
+<histogram name="Blink.BudgetAPI.QueryBudget" units="budget">
+  <owner>harkness@chromium.org</owner>
+  <summary>
+    Whenever the Budget API framework receives a query for the current budget,
+    this records the total budget available to the origin, which is an internal
+    Chrome value for the amount of background processing an origin can do
+    without visibly alerting the user. Scale for the budget is 0 to 100. Care
+    should be taken when drawing conclusions from this metric, as budget is
+    based on both engagement and usage, so could vary significantly based on
+    user behaviour and origin.
+  </summary>
+</histogram>
+
+<histogram name="Blink.BudgetAPI.Reserve" enum="BooleanSuccess">
+  <owner>harkness@chromium.org</owner>
+  <summary>
+    Whenever the Budget API framework receives a request to reserve budget for a
+    future background operation, this records whether the reserve request
+    succeeded or not.
+  </summary>
+</histogram>
+
 <histogram name="Blink.Canvas.DrawImage" units="microseconds">
   <owner>junov@chromium.org</owner>
   <summary>Time spent on 2D canvas drawImage API call.</summary>