Add a flag to over approximate the weak closure during GC

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 741 matching lines @@
       AllocationSpace space, const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   static const int kNoGCFlags = 0;
   static const int kReduceMemoryFootprintMask = 1;
   static const int kAbortIncrementalMarkingMask = 2;
 
   // Making the heap iterable requires us to abort incremental marking.
   static const int kMakeHeapIterableMask = kAbortIncrementalMarkingMask;
 
+  // Invoked when GC was requested via the stack guard.
+  void HandleGCRequest();
+
+  // Attempt to over-approximate the weak closure by marking object groups and
+  // implicit references from global handles, but don't atomically complete
+  // marking. If we continue to mark incrementally, we might have marked
+  // objects that die later.
+  void OverApproximateWeakClosure(const char* gc_reason);
+
   // Performs a full garbage collection.  If (flags & kMakeHeapIterableMask) is
   // non-zero, then the slower precise sweeper is used, which leaves the heap
   // in a state where we can iterate over the heap visiting all objects.
   void CollectAllGarbage(
       int flags, const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   // Last hope GC, should try to squeeze as much as possible.
   void CollectAllAvailableGarbage(const char* gc_reason = NULL);
 
@@ skipping 1813 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_