bug 1473333 - add Telemetry probe HTTP_CHANNEL_ONSTART_SUCCESS r=mcmanus

Measure success rate in nsHttpChannel::OnStartRequest

MozReview-Commit-ID: Ia8h8acIvSA

netwerk/protocol/http/nsHttpChannel.cpp

@@ -6879,6 +6879,9 @@ nsHttpChannel::OnStartRequest(nsIRequest *request, nsISupports *ctxt)
     LOG(("nsHttpChannel::OnStartRequest [this=%p request=%p status=%" PRIx32 "]\n",
          this, request, static_cast<uint32_t>(static_cast<nsresult>(mStatus))));
 
+    Telemetry::Accumulate(Telemetry::HTTP_CHANNEL_ONSTART_SUCCESS,
+                          NS_SUCCEEDED(mStatus));
+
     if (mRaceCacheWithNetwork) {
         LOG(("  racingNetAndCache - mFirstResponseSource:%d fromCache:%d fromNet:%d\n",
              static_cast<int32_t>(mFirstResponseSource), request == mCachePump, request == mTransactionPump));

toolkit/components/telemetry/Histograms.json

@@ -2465,6 +2465,14 @@
     "description": "Upgrading display content Channel Disposition",
     "labels": ["cancel", "disk", "netOk", "netEarlyFail", "netLateFail"]
   },
+  "HTTP_CHANNEL_ONSTART_SUCCESS" : {
+    "record_in_processes": ["main"],
+    "expires_in_version": "never",
+    "kind": "boolean",
+    "description": "Successfully started HTTP channels",
+    "bug_numbers": [1473333],
+    "alert_emails": ["necko@mozilla.com", "dstenberg@mozilla.com"]
+  },
   "HTTP_CONNECTION_ENTRY_CACHE_HIT_1" : {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",