Bug 1689156 - Don't generate first-contentful-paint if the paint doesn't come from Tick r=smaug

When a contentful paint occurs which doesn't come from Tick, we should
not generate a first-contentful-paint entry for it because
    1) It violates the spec
    2) It usually means some magical paints which we should not expose
    to the web.

So this patches stop generating a contentful paint entry for that,
instead asking the next tick to generate the entry.

Depends on D107858

Differential Revision: https://phabricator.services.mozilla.com/D107859

layout/base/nsPresContext.cpp

@@ -220,6 +220,7 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
       mQuirkSheetAdded(false),
       mHadNonBlankPaint(false),
       mHadContentfulPaint(false),
+      mHadNonTickContentfulPaint(false),
       mHadContentfulPaintComposite(false)
 #ifdef DEBUG
       ,
@@ -2422,33 +2423,42 @@ void nsPresContext::NotifyNonBlankPaint() {
 }
 
 void nsPresContext::NotifyContentfulPaint() {
+  nsRootPresContext* rootPresContext = GetRootPresContext();
+  if (!rootPresContext) {
+    return;
+  }
   if (!mHadContentfulPaint) {
 #if defined(MOZ_WIDGET_ANDROID)
-    (new AsyncEventDispatcher(mDocument, u"MozFirstContentfulPaint"_ns,
-                              CanBubble::eYes, ChromeOnlyDispatch::eYes))
-        ->PostDOMEvent();
+    if (!mHadNonTickContentfulPaint) {
+      (new AsyncEventDispatcher(mDocument, u"MozFirstContentfulPaint"_ns,
+                                CanBubble::eYes, ChromeOnlyDispatch::eYes))
+          ->PostDOMEvent();
+    }
 #endif
+    if (!rootPresContext->RefreshDriver()->IsInRefresh()) {
+      if (!mHadNonTickContentfulPaint) {
+        rootPresContext->RefreshDriver()
+            ->AddForceNotifyContentfulPaintPresContext(this);
+        mHadNonTickContentfulPaint = true;
+      }
+      return;
+    }
     mHadContentfulPaint = true;
-    if (nsRootPresContext* rootPresContext = GetRootPresContext()) {
-      mFirstContentfulPaintTransactionId =
-          Some(rootPresContext->mRefreshDriver->LastTransactionId().Next());
-      if (nsPIDOMWindowInner* innerWindow = mDocument->GetInnerWindow()) {
-        if (Performance* perf = innerWindow->GetPerformance()) {
-          TimeStamp nowTime =
-              rootPresContext->RefreshDriver()->MostRecentRefresh(
-                  /* aEnsureTimerStarted */ false);
-          MOZ_ASSERT(
-              !nowTime.IsNull(),
-              "Most recent refresh timestamp should exist since we are in "
-              "a refresh driver tick");
-          MOZ_ASSERT(rootPresContext->RefreshDriver()->IsInRefresh(),
-                     "We should only notify contentful paint during refresh "
-                     "driver ticks");
-          RefPtr<PerformancePaintTiming> paintTiming =
-              new PerformancePaintTiming(perf, u"first-contentful-paint"_ns,
-                                         nowTime);
-          perf->SetFCPTimingEntry(paintTiming);
-        }
+    mFirstContentfulPaintTransactionId =
+        Some(rootPresContext->mRefreshDriver->LastTransactionId().Next());
+    if (nsPIDOMWindowInner* innerWindow = mDocument->GetInnerWindow()) {
+      if (Performance* perf = innerWindow->GetPerformance()) {
+        TimeStamp nowTime = rootPresContext->RefreshDriver()->MostRecentRefresh(
+            /* aEnsureTimerStarted */ false);
+        MOZ_ASSERT(!nowTime.IsNull(),
+                   "Most recent refresh timestamp should exist since we are in "
+                   "a refresh driver tick");
+        MOZ_ASSERT(rootPresContext->RefreshDriver()->IsInRefresh(),
+                   "We should only notify contentful paint during refresh "
+                   "driver ticks");
+        RefPtr<PerformancePaintTiming> paintTiming = new PerformancePaintTiming(
+            perf, u"first-contentful-paint"_ns, nowTime);
+        perf->SetFCPTimingEntry(paintTiming);
       }
     }
   }
@@ -2462,6 +2472,7 @@ void nsPresContext::NotifyPaintStatusReset() {
                             CanBubble::eYes, ChromeOnlyDispatch::eYes))
       ->PostDOMEvent();
 #endif
+  mHadNonTickContentfulPaint = false;
 }
 
 void nsPresContext::NotifyDOMContentFlushed() {

layout/base/nsPresContext.h

@@ -1331,6 +1331,11 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   unsigned mHadNonBlankPaint : 1;
   // Has NotifyContentfulPaint been called on this PresContext?
   unsigned mHadContentfulPaint : 1;
+  // True when a contentful paint has happened and this paint doesn't
+  // come from the regular tick process. Usually this means a
+  // contentful paint was triggered manually.
+  unsigned mHadNonTickContentfulPaint : 1;
+
   // Has NotifyDidPaintForSubtree been called for a contentful paint?
   unsigned mHadContentfulPaintComposite : 1;
 

layout/base/nsRefreshDriver.cpp

@@ -1355,6 +1355,21 @@ void nsRefreshDriver::RegisterCompositionPayload(
   mCompositionPayloads.AppendElement(aPayload);
 }
 
+void nsRefreshDriver::AddForceNotifyContentfulPaintPresContext(
+    nsPresContext* aPresContext) {
+  mForceNotifyContentfulPaintPresContexts.AppendElement(aPresContext);
+}
+
+void nsRefreshDriver::FlushForceNotifyContentfulPaintPresContext() {
+  while (!mForceNotifyContentfulPaintPresContexts.IsEmpty()) {
+    WeakPtr<nsPresContext> presContext =
+        mForceNotifyContentfulPaintPresContexts.PopLastElement();
+    if (presContext) {
+      presContext->NotifyContentfulPaint();
+    }
+  }
+}
+
 void nsRefreshDriver::RunDelayedEventsSoon() {
   // Place entries for delayed events into their corresponding normal list,
   // and schedule a refresh. When these delayed events run, if their document
@@ -2033,6 +2048,8 @@ void nsRefreshDriver::Tick(VsyncId aId, TimeStamp aNowTime) {
     DisplayPortUtils::UpdateDisplayPortMarginsFromPendingMessages();
   }
 
+  FlushForceNotifyContentfulPaintPresContext();
+
   AutoTArray<nsCOMPtr<nsIRunnable>, 16> earlyRunners = std::move(mEarlyRunners);
   for (auto& runner : earlyRunners) {
     runner->Run();

layout/base/nsRefreshDriver.h

@@ -407,6 +407,9 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
     eHasVisualViewportScrollEvents = 1 << 5,
   };
 
+  void AddForceNotifyContentfulPaintPresContext(nsPresContext* aPresContext);
+  void FlushForceNotifyContentfulPaintPresContext();
+
  private:
   typedef nsTArray<RefPtr<VVPResizeEvent>> VisualViewportResizeEventArray;
   typedef nsTArray<RefPtr<mozilla::Runnable>> ScrollEventArray;
@@ -588,6 +591,17 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
   AutoTArray<mozilla::AnimationEventDispatcher*, 16>
       mAnimationEventFlushObservers;
 
+  // nsPresContexts which `NotifyContentfulPaint` have been called,
+  // however the corresponding paint doesn't come from a regular
+  // rendering steps(aka tick).
+  //
+  // For these nsPresContexts, we invoke
+  // `FlushForceNotifyContentfulPaintPresContext` in the next tick
+  // to force notify contentful paint, regardless whether the tick paints
+  // or not.
+  nsTArray<mozilla::WeakPtr<nsPresContext>>
+      mForceNotifyContentfulPaintPresContexts;
+
   void BeginRefreshingImages(RequestTable& aEntries,
                              mozilla::TimeStamp aDesired);
 

layout/painting/nsDisplayList.cpp

@@ -1178,8 +1178,7 @@ void nsDisplayListBuilder::LeavePresShell(const nsIFrame* aReferenceFrame,
       }
     }
     nsRootPresContext* rootPresContext = pc->GetRootPresContext();
-    if (!pc->HadContentfulPaint() && rootPresContext &&
-        rootPresContext->RefreshDriver()->IsInRefresh()) {
+    if (!pc->HadContentfulPaint() && rootPresContext) {
       if (!CurrentPresShellState()->mIsBackgroundOnly) {
         if (pc->HasEverBuiltInvisibleText() ||
             DisplayListIsContentful(this, aPaintedContents)) {