[heap] Allow repeatedly setting EmbedderHeapTracer

src/heap/heap.cc

 // 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.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/context-slot-cache.h"
 #include "src/base/bits.h"
@@ skipping 5534 matching lines @@
     for (Page* p : *s) {
       CHECK(p->NeverEvacuate());
     }
 #endif  // DEBUG
   }
 
   deserialization_complete_ = true;
 }
 
 void Heap::SetEmbedderHeapTracer(EmbedderHeapTracer* tracer) {
-  DCHECK_NOT_NULL(tracer);
-  CHECK_NULL(embedder_heap_tracer_);
+  DCHECK_EQ(gc_state_, HeapState::NOT_IN_GC);
   embedder_heap_tracer_ = tracer;
 }
 
 void Heap::RegisterWrappersWithEmbedderHeapTracer() {
   DCHECK(UsingEmbedderHeapTracer());
   if (wrappers_to_trace_.empty()) {
     return;
   }
   embedder_heap_tracer()->RegisterV8References(wrappers_to_trace_);
   wrappers_to_trace_.clear();
@@ skipping 920 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8