Add a flag to over approximate the weak closure during GC

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index cec871403a718d8f2a88b8666af713e48ba56f54..16c6c5ad0e2b811d48d9c2dcc666f8081792626c 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -735,6 +735,48 @@ void Heap::GarbageCollectionEpilogue() {
 }
 
 
+void Heap::HandleGCRequest() {
+  if (incremental_marking()->IsComplete()) {
+    CollectAllGarbage(Heap::kNoGCFlags, "GC interrupt");
+    return;
+  }
+  DCHECK(FLAG_overapproximate_weak_closure);
+  DCHECK(!incremental_marking()->weak_closure_was_overapproximated());
+  OverApproximateWeakClosure("GC interrupt");
+}
+
+
+void Heap::OverApproximateWeakClosure(const char* gc_reason) {
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Overapproximate weak closure (%s).\n",
+           gc_reason);
+  }
+  {
+    GCCallbacksScope scope(this);
+    if (scope.CheckReenter()) {
+      AllowHeapAllocation allow_allocation;
+      GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
+      VMState<EXTERNAL> state(isolate_);
+      HandleScope handle_scope(isolate_);
+      CallGCPrologueCallbacks(kGCTypeMarkSweepCompact, kNoGCCallbackFlags);
+    }
+  }
+  mark_compact_collector()->OverApproximateWeakClosure();
+  incremental_marking()->set_should_hurry(false);
+  incremental_marking()->set_weak_closure_was_overapproximated(true);
+  {
+    GCCallbacksScope scope(this);
+    if (scope.CheckReenter()) {
+      AllowHeapAllocation allow_allocation;
+      GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
+      VMState<EXTERNAL> state(isolate_);
+      HandleScope handle_scope(isolate_);
+      CallGCEpilogueCallbacks(kGCTypeMarkSweepCompact, kNoGCCallbackFlags);
+    }
+  }
+}
+
+
 void Heap::CollectAllGarbage(int flags, const char* gc_reason,
                              const v8::GCCallbackFlags gc_callback_flags) {
   // Since we are ignoring the return value, the exact choice of space does