Stop JankTracker when FrameView is disposed.

This prevents spurious trace events from the empty document created
before navigation begins.

Also annotate trace events with the frame they correspond to, combine
score and max distance into a single TracedValue, and change trace
category to "loading".

Bug: 581518
Change-Id: I9ee8005596245ad31c78a8556ec837e2ef999d24
Reviewed-on: https://chromium-review.googlesource.com/1101245Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567383}

third_party/blink/renderer/core/frame/local_frame_view.cc

@@ -436,6 +436,7 @@ void LocalFrameView::Dispose() {
   ClearPrintContext();
 
   ukm_time_aggregator_.reset();
+  jank_tracker_.Dispose();
 
 #if DCHECK_IS_ON()
   has_been_disposed_ = true;

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

@@ -133,7 +133,7 @@ void JankTracker::NotifyPrePaintFinished() {
   DVLOG(1) << "viewport " << (jank_fraction * 100)
            << "% janked, raising score to " << score_;
 
-  TRACE_EVENT_INSTANT1("blink", "FrameLayoutJank", TRACE_EVENT_SCOPE_THREAD,
+  TRACE_EVENT_INSTANT1("loading", "FrameLayoutJank", TRACE_EVENT_SCOPE_THREAD,
                        "viewportFraction", jank_fraction);
 
   region_ = Region();
@@ -153,6 +153,13 @@ bool JankTracker::IsActive() {
   return true;
 }
 
+std::unique_ptr<TracedValue> JankTracker::TraceData() const {
+  std::unique_ptr<TracedValue> value = TracedValue::Create();
+  value->SetDouble("score", score_);
+  value->SetDouble("maxDistance", max_distance_);
+  return value;
+}
+
 void JankTracker::TimerFired(TimerBase* timer) {
   has_fired_ = true;
 
@@ -165,8 +172,9 @@ void JankTracker::TimerFired(TimerBase* timer) {
            << " is " << score_ << " with max move distance of "
            << max_distance_;
 
-  TRACE_EVENT_INSTANT2("blink", "TotalLayoutJank", TRACE_EVENT_SCOPE_THREAD,
-                       "score", score_, "maxDistance", max_distance_);
+  TRACE_EVENT_INSTANT2("loading", "TotalLayoutJank", TRACE_EVENT_SCOPE_THREAD,
+                       "data", TraceData(), "frame",
+                       ToTraceValue(&frame_view_->GetFrame()));
 }
 
 }  // namespace blink

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

@@ -16,6 +16,7 @@ class LayoutObject;
 class LayoutRect;
 class LocalFrameView;
 class PaintLayer;
+class TracedValue;
 
 // Tracks "jank" from layout objects changing their visual location between
 // animation frames.
@@ -32,9 +33,11 @@ class CORE_EXPORT JankTracker {
   bool IsActive();
   double Score() const { return score_; }
   float MaxDistance() const { return max_distance_; }
+  void Dispose() { timer_.Stop(); }
 
  private:
   void TimerFired(TimerBase*);
+  std::unique_ptr<TracedValue> TraceData() const;
 
   // This owns us.
   UntracedMember<LocalFrameView> frame_view_;