Slow down incremental marking on main thread when idle notification is active.

src/heap/heap.h

 // Copyright 2012 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.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 
 #include "src/allocation.h"
@@ skipping 1277 matching lines @@
 
   inline void DoScavengeObject(Map* map, HeapObject** slot, HeapObject* obj) {
     scavenging_visitors_table_.GetVisitor(map)(map, slot, obj);
   }
 
   void QueueMemoryChunkForFree(MemoryChunk* chunk);
   void FreeQueuedChunks();
 
   int gc_count() const { return gc_count_; }
 
+  bool RecentIdleNotifcationHappened();
+
   // Completely clear the Instanceof cache (to stop it keeping objects alive
   // around a GC).
   inline void CompletelyClearInstanceofCache();
 
   // The roots that have an index less than this are always in old space.
   static const int kOldSpaceRoots = 0x20;
 
   uint32_t HashSeed() {
     uint32_t seed = static_cast<uint32_t>(hash_seed()->value());
     DCHECK(FLAG_randomize_hashes || seed == 0);
@@ skipping 742 matching lines @@
 
   // Minimal interval between two subsequent collections.
   double min_in_mutator_;
 
   // Cumulative GC time spent in marking
   double marking_time_;
 
   // Cumulative GC time spent in sweeping
   double sweeping_time_;
 
+  // Last time an idle notification happened
+  double last_idle_notification_time_;
+
   MarkCompactCollector mark_compact_collector_;
 
   StoreBuffer store_buffer_;
 
   Marking marking_;
 
   IncrementalMarking incremental_marking_;
 
   GCIdleTimeHandler gc_idle_time_handler_;
   unsigned int gc_count_at_last_idle_gc_;
@@ skipping 509 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_