Bug 1460589 - Add DNS vs TRR success/fail telemetry counter. r=mcmanus

netwerk/dns/nsHostResolver.cpp

@@ -298,6 +298,15 @@ nsHostRecord::ResolveComplete()
         }
     }
 
+    if (mTRRUsed && mNativeUsed) {
+        // both were used, accumulate comparative success
+        AccumulateCategorical(mNativeSuccess && mTRRSuccess?
+                              Telemetry::LABELS_DNS_TRR_COMPARE::BothWorked :
+                              ((mNativeSuccess ? Telemetry::LABELS_DNS_TRR_COMPARE::NativeWorked :
+                                (mTRRSuccess ? Telemetry::LABELS_DNS_TRR_COMPARE::TRRWorked:
+                                 Telemetry::LABELS_DNS_TRR_COMPARE::BothFailed))));
+    }
+
     switch(mResolverMode) {
     case MODE_NATIVEONLY:
     case MODE_TRROFF:

toolkit/components/telemetry/Histograms.json

@@ -3283,6 +3283,15 @@
     "bug_numbers": [1434852],
     "description": "DNS: TRR parallel resolve racing results"
   },
+  "DNS_TRR_COMPARE": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["necko@mozilla.com", "dstenberg@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "categorical",
+    "labels": ["BothWorked", "NativeWorked", "TRRWorked", "BothFailed"],
+    "bug_numbers": [1460589],
+    "description": "DNS: success distribution when both native and TRR were used"
+  },
   "DNS_TRR_BLACKLISTED": {
     "record_in_processes": ["main"],
     "expires_in_version": "never",