Add GC stats to GC timeline events

runtime/vm/heap.h

Index: runtime/vm/heap.h
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index 1526424a91cccf1a3b5c5f07a55607caa1a0d3ac..c5a7693934030d167b554fcfba1b898c948ddbe6 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -22,6 +22,7 @@ class Isolate;
 class ObjectPointerVisitor;
 class ObjectSet;
 class ServiceEvent;
+class TimelineEventScope;
 class VirtualMemory;
 
 class Heap {
@@ -327,6 +328,7 @@ class Heap {
   void PrintStats();
   void UpdateClassHeapStatsBeforeGC(Heap::Space space);
   void UpdatePretenurePolicy();
+  void PrintStatsToTimeline(TimelineEventScope* event);
 
   // Updates gc in progress flags.
   bool BeginNewSpaceGC(Thread* thread);