[heap] Remove unused no marking scope.

BUG=

Review URL: https://codereview.chromium.org/1849613004

Cr-Commit-Position: refs/heads/master@{#35155}

src/heap/incremental-marking.cc

@@ -39,7 +39,6 @@ IncrementalMarking::IncrementalMarking(Heap* heap)
       allocated_(0),
       write_barriers_invoked_since_last_step_(0),
       idle_marking_delay_counter_(0),
-      no_marking_scope_depth_(0),
       unscanned_bytes_of_large_object_(0),
       was_activated_(false),
       black_allocation_(false),
@@ -1151,8 +1150,6 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
     return 0;
   }
 
-  if (state_ == MARKING && no_marking_scope_depth_ > 0) return 0;
-
   intptr_t bytes_processed = 0;
   {
     HistogramTimerScope incremental_marking_scope(

src/heap/incremental-marking.h

@@ -194,10 +194,6 @@ class IncrementalMarking {
 
   void NotifyOfHighPromotionRate();
 
-  void EnterNoMarkingScope() { no_marking_scope_depth_++; }
-
-  void LeaveNoMarkingScope() { no_marking_scope_depth_--; }
-
   void NotifyIncompleteScanOfObject(int unscanned_bytes) {
     unscanned_bytes_of_large_object_ = unscanned_bytes;
   }
@@ -291,8 +287,6 @@ class IncrementalMarking {
   intptr_t write_barriers_invoked_since_last_step_;
   size_t idle_marking_delay_counter_;
 
-  int no_marking_scope_depth_;
-
   int unscanned_bytes_of_large_object_;
 
   bool was_activated_;