Bug 1377251 - Expose TIME_TO_NON_BLANK_PAINT as Performance Entry behind pref. r=qDot

dom/base/nsDOMNavigationTiming.h

@@ -82,6 +82,14 @@ public:
   {
     return mLoadEventEnd;
   }
+  DOMTimeMilliSec GetTimeToNonBlankPaint() const
+  {
+    if (mNonBlankPaintTimeStamp.IsNull()) {
+      return 0;
+    }
+
+    return TimeStampToDOMHighRes(mNonBlankPaintTimeStamp);
+  }
 
   enum class DocShellState : uint8_t {
     eActive,
@@ -110,7 +118,7 @@ public:
 
   DOMTimeMilliSec TimeStampToDOM(mozilla::TimeStamp aStamp) const;
 
-  inline DOMHighResTimeStamp TimeStampToDOMHighRes(mozilla::TimeStamp aStamp)
+  inline DOMHighResTimeStamp TimeStampToDOMHighRes(mozilla::TimeStamp aStamp) const
   {
     mozilla::TimeDuration duration = aStamp - mNavigationStartTimeStamp;
     return duration.ToMilliseconds();

dom/performance/PerformanceTiming.h

@@ -244,6 +244,15 @@ public:
     return GetDOMTiming()->GetLoadEventEnd();
   }
 
+  DOMTimeMilliSec TimeToNonBlankPaint() const
+  {
+    if (!nsContentUtils::IsPerformanceTimingEnabled() ||
+        nsContentUtils::ShouldResistFingerprinting()) {
+      return 0;
+    }
+    return GetDOMTiming()->GetTimeToNonBlankPaint();
+  }
+
 private:
   ~PerformanceTiming();
 

dom/webidl/PerformanceTiming.webidl

@@ -34,5 +34,11 @@ interface PerformanceTiming {
   readonly attribute unsigned long long loadEventStart;
   readonly attribute unsigned long long loadEventEnd;
 
+  // This is a Chrome proprietary extension and not part of the
+  // performance/navigation timing specification.
+  // Returns 0 if a non-blank paint has not happened.
+  [Pref="dom.performance.time_to_non_blank_paint.enabled"]
+  readonly attribute unsigned long long timeToNonBlankPaint;
+
   jsonifier;
 };

modules/libpref/init/all.js

@@ -180,6 +180,9 @@ pref("dom.performance.enable_notify_performance_timing", false);
 // Enable Permission API's .revoke() method
 pref("dom.permissions.revoke.enable", false);
 
+// Enable exposing timeToNonBlankPaint
+pref("dom.performance.time_to_non_blank_paint.enabled", false);
+
 // Enable Performance Observer API
 #ifdef NIGHTLY_BUILD
 pref("dom.enable_performance_observer", true);