Bug 1313686 - Add opt-out Telemetry probe to see how long it takes for TabChild::RecvSetDocShellIsActive to paint a tab. data-review=liuche, r=billm,liuche

MozReview-Commit-ID: 5B588cs3cJ8

--HG--
extra : rebase_source : 8a7a7ec513e48e673f4c52a417aeacc037785617

dom/ipc/TabChild.cpp

@@ -2449,6 +2449,7 @@ TabChild::RecvSetDocShellIsActive(const bool& aIsActive,
         root->SchedulePaint();
       }
 
+      Telemetry::AutoTimer<Telemetry::TABCHILD_PAINT_TIME> timer;
       // If we need to repaint, let's do that right away. No sense waiting until
       // we get back to the event loop again. We suppress the display port so that
       // we only paint what's visible. This ensures that the tab we're switching

toolkit/components/telemetry/Histograms.json

@@ -10447,5 +10447,15 @@
     "n_buckets": 50,
     "bug_numbers": [1301346],
     "description": "The time spent handling beforeunload event in milliseconds. It measures all documents and subframes separately. If there are multiple handlers for the unload event in a document, this will record a single value across all handlers in the document."
+  },
+  "TABCHILD_PAINT_TIME": {
+    "alert_emails": ["mconley@mozilla.com"],
+    "bug_numbers": [1313686],
+    "expires_in_version": "56",
+    "kind": "exponential",
+    "high": 1000,
+    "n_buckets": 50,
+    "description": "Time spent painting the contents of a remote browser (ms).",
+    "releaseChannelCollection": "opt-out"
   }
 }