Bug 1515132: Add telemetry for FirstContentfulPaint data-review=chutt…

…en r=mstange, a=lizzard

Defined in the PerformancePaintTiming spec, though we're not supporting the
DOM API yet

--HG--
extra : source : 134b85ae973cb92917cedc21ac624e75a8f27406

dom/base/nsDOMNavigationTiming.cpp

@@ -458,6 +458,11 @@ void nsDOMNavigationTiming::NotifyContentfulPaintForRootContentDocument() {
                                        TTI_WINDOW_SIZE_MS,
                                        nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY,
                                        "nsDOMNavigationTiming::TTITimeout");
+
+  if (mDocShellHasBeenActiveSinceNavigationStart) {
+    Telemetry::AccumulateTimeDelta(Telemetry::TIME_TO_FIRST_CONTENTFUL_PAINT_MS,
+                                   mNavigationStart, mContentfulPaint);
+  }
 }
 
 void nsDOMNavigationTiming::NotifyDOMContentFlushedForRootContentDocument() {

toolkit/components/telemetry/Histograms.json

@@ -13369,6 +13369,17 @@
     "bug_numbers": [1411632],
     "description": "The time between navigation start and the first non-blank paint of a foreground root content document, in milliseconds. This only records documents that were in an active docshell throughout the whole time between navigation start and non-blank paint. The non-blank paint timestamp is taken during display list building and does not include rasterization or compositing of that paint.  This probe only accumulates when there were no active-tab network load optimizations happening during the interval."
   },
+  "TIME_TO_FIRST_CONTENTFUL_PAINT_MS": {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["[email protected]", "[email protected]", "[email protected]", "[email protected]"],
+    "expires_in_version": "never",
+    "releaseChannelCollection": "opt-out",
+    "kind": "exponential",
+    "high": 100000,
+    "n_buckets": 100,
+    "bug_numbers": [1515132],
+    "description": "The time between navigation start and the first contentful paint of a foreground root content document, in milliseconds. This only records documents that were in an active docshell throughout the whole time between navigation start and contentful paint. The contentful paint timestamp is taken during display list building and does not include rasterization or compositing of that paint."
+  },
   "TAB_AUDIO_INDICATOR_USED": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["[email protected]"],