re-land: Track history of events in GCTracer.

src/incremental-marking.h

Index: src/incremental-marking.h
diff --git a/src/incremental-marking.h b/src/incremental-marking.h
index bed8e185d6411ca1e464492e64bcbd65862c580f..20cfb018ae368b5a47504ebcd59a7a21dab654a1 100644
--- a/src/incremental-marking.h
+++ b/src/incremental-marking.h
@@ -136,16 +136,6 @@ class IncrementalMarking {
 
   inline void WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit);
 
-  inline int steps_count() { return steps_count_; }
-
-  inline double steps_took() { return steps_took_; }
-
-  inline double longest_step() { return longest_step_; }
-
-  inline int steps_count_since_last_gc() { return steps_count_since_last_gc_; }
-
-  inline double steps_took_since_last_gc() { return steps_took_since_last_gc_; }
-
   inline void SetOldSpacePageFlags(MemoryChunk* chunk) {
     SetOldSpacePageFlags(chunk, IsMarking(), IsCompacting());
   }
@@ -226,12 +216,8 @@ class IncrementalMarking {
   MarkingDeque marking_deque_;
 
   int steps_count_;
-  double steps_took_;
-  double longest_step_;
   int64_t old_generation_space_available_at_start_of_incremental_;
   int64_t old_generation_space_used_at_start_of_incremental_;
-  int steps_count_since_last_gc_;
-  double steps_took_since_last_gc_;
   int64_t bytes_rescanned_;
   bool should_hurry_;
   int marking_speed_;