Extract some layout shift reporting steps into a helper.

These steps will need to be deferred for pointerdown buffering.

Also expand logging to indicate when layout shifts were ignored due to
recent input.

Bug: 978027
Change-Id: I9beca66d9d626de8f1327d730e41ed9bdebbcfa1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715228Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680446}

third_party/blink/renderer/core/layout/layout_shift_tracker.cc

@@ -203,7 +203,7 @@ void LayoutShiftTracker::ObjectShifted(
 
 #if DCHECK_IS_ON()
   LocalFrame& frame = frame_view_->GetFrame();
-  if (!HadRecentInput() && ShouldLog(frame)) {
+  if (ShouldLog(frame)) {
     DVLOG(2) << "in " << (frame.IsMainFrame() ? "" : "subframe ")
              << frame.GetDocument()->Url().GetString() << ", "
              << source.DebugName() << " moved from " << old_rect.ToString()
@@ -307,28 +307,44 @@ void LayoutShiftTracker::NotifyPrePaintFinished() {
           ? double(frame_max_distance_) / viewport_max_dimension
           : 1.0;
   double score_delta = impact_fraction * move_distance_factor;
-
-  if (!HadRecentInput())
-    score_ += score_delta;
+  double weighted_score_delta = score_delta * SubframeWeightingFactor();
 
   overall_max_distance_ = std::max(overall_max_distance_, frame_max_distance_);
 
-  LocalFrame& frame = frame_view_->GetFrame();
 #if DCHECK_IS_ON()
-  if (!HadRecentInput() && ShouldLog(frame)) {
+  LocalFrame& frame = frame_view_->GetFrame();
+  if (ShouldLog(frame)) {
     DVLOG(1) << "in " << (frame.IsMainFrame() ? "" : "subframe ")
              << frame.GetDocument()->Url().GetString() << ", viewport was "
              << (impact_fraction * 100) << "% impacted with distance fraction "
-             << move_distance_factor << "; raising score to " << score_;
+             << move_distance_factor;
   }
 #endif
 
-  TRACE_EVENT_INSTANT2("loading", "LayoutShift", TRACE_EVENT_SCOPE_THREAD,
-                       "data", PerFrameTraceData(score_delta, HadRecentInput()),
-                       "frame", ToTraceValue(&frame));
+  ReportShift(score_delta, weighted_score_delta);
+
+  if (use_sweep_line) {
+    if (!region_experimental_.IsEmpty() && !HadRecentInput()) {
+      SetLayoutShiftRects(region_experimental_.GetRects(), 1, true);
+    }
+    region_experimental_.Reset();
+  } else {
+    if (!region_.IsEmpty() && !HadRecentInput()) {
+      SetLayoutShiftRects(region_.Rects(), granularity_scale, false);
+    }
+    region_ = Region();
+  }
+  frame_max_distance_ = 0.0;
+  frame_scroll_delta_ = ScrollOffset();
+}
 
-  if (!HadRecentInput()) {
-    double weighted_score_delta = score_delta * SubframeWeightingFactor();
+void LayoutShiftTracker::ReportShift(double score_delta,
+                                     double weighted_score_delta) {
+  LocalFrame& frame = frame_view_->GetFrame();
+  bool had_recent_input = HadRecentInput();
+
+  if (!had_recent_input) {
+    score_ += score_delta;
     if (weighted_score_delta > 0) {
       weighted_score_ += weighted_score_delta;
       frame.Client()->DidObserveLayoutShift(weighted_score_delta,
@@ -342,24 +358,24 @@ void LayoutShiftTracker::NotifyPrePaintFinished() {
     WindowPerformance* performance =
         DOMWindowPerformance::performance(*frame.DomWindow());
     if (performance) {
-      performance->AddLayoutJankFraction(score_delta, HadRecentInput(),
+      performance->AddLayoutJankFraction(score_delta, had_recent_input,
                                          most_recent_input_timestamp_);
     }
   }
 
-  if (use_sweep_line) {
-    if (!region_experimental_.IsEmpty() && !HadRecentInput()) {
-      SetLayoutShiftRects(region_experimental_.GetRects(), 1, true);
-    }
-    region_experimental_.Reset();
-  } else {
-    if (!region_.IsEmpty() && !HadRecentInput()) {
-      SetLayoutShiftRects(region_.Rects(), granularity_scale, false);
-    }
-    region_ = Region();
+  TRACE_EVENT_INSTANT2("loading", "LayoutShift", TRACE_EVENT_SCOPE_THREAD,
+                       "data", PerFrameTraceData(score_delta, had_recent_input),
+                       "frame", ToTraceValue(&frame));
+
+#if DCHECK_IS_ON()
+  if (ShouldLog(frame)) {
+    DVLOG(1) << "in " << (frame.IsMainFrame() ? "" : "subframe ")
+             << frame.GetDocument()->Url().GetString() << ", layout shift of "
+             << score_delta
+             << (had_recent_input ? " excluded by recent input" : " reported")
+             << "; cumulative score is " << score_;
   }
-  frame_max_distance_ = 0.0;
-  frame_scroll_delta_ = ScrollOffset();
+#endif
 }
 
 void LayoutShiftTracker::NotifyInput(const WebInputEvent& event) {

third_party/blink/renderer/core/layout/layout_shift_tracker.h

@@ -58,6 +58,7 @@ class CORE_EXPORT LayoutShiftTracker {
                      const PropertyTreeState&,
                      FloatRect old_rect,
                      FloatRect new_rect);
+  void ReportShift(double score_delta, double weighted_score_delta);
   void TimerFired(TimerBase*) {}
   std::unique_ptr<TracedValue> PerFrameTraceData(double score_delta,
                                                  bool input_detected) const;