Don't assert that no incremental marking happened during a non-incremental GC

src/heap/gc-tracer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/heap/gc-tracer.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 200 matching lines @@
     current_.pure_incremental_marking_duration =
         current_.cumulative_pure_incremental_marking_duration -
         previous_incremental_mark_compactor_event_
             .cumulative_pure_incremental_marking_duration;
     longest_incremental_marking_step_ = 0.0;
     incremental_mark_compactor_events_.push_front(current_);
   } else {
     DCHECK(current_.incremental_marking_bytes == 0);
     DCHECK(current_.incremental_marking_duration == 0);
     DCHECK(current_.pure_incremental_marking_duration == 0);
-    DCHECK(longest_incremental_marking_step_ == 0.0);
+    longest_incremental_marking_step_ = 0.0;
     mark_compactor_events_.push_front(current_);
   }
 
   // TODO(ernstm): move the code below out of GCTracer.
 
   if (!FLAG_trace_gc && !FLAG_print_cumulative_gc_stat) return;
 
   double duration = current_.end_time - current_.start_time;
   double spent_in_mutator = Max(current_.start_time - previous_.end_time, 0.0);
 
@@ skipping 355 matching lines @@
 
 
 bool GCTracer::SurvivalEventsRecorded() const {
   return survival_events_.size() > 0;
 }
 
 
 void GCTracer::ResetSurvivalEvents() { survival_events_.reset(); }
 }
 }  // namespace v8::internal