[serializer] make snapshot reproducible.

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 <map>
 
@@ skipping 986 matching lines @@
 
   void SetRootNoScriptSharedFunctionInfos(Object* value) {
     roots_[kNoScriptSharedFunctionInfosRootIndex] = value;
   }
 
   // Set the stack limit in the roots_ array.  Some architectures generate
   // code that looks here, because it is faster than loading from the static
   // jslimit_/real_jslimit_ variable in the StackGuard.
   void SetStackLimits();
 
+  // The stack limit is thread-dependent. To be able to reproduce the same
+  // snapshot blob, we need to reset it before serializing.
+  void ClearStackLimits();
+
   // Generated code can treat direct references to this root as constant.
   bool RootCanBeTreatedAsConstant(RootListIndex root_index);
 
   Map* MapForFixedTypedArray(ExternalArrayType array_type);
   RootListIndex RootIndexForFixedTypedArray(ExternalArrayType array_type);
 
   RootListIndex RootIndexForEmptyFixedTypedArray(ElementsKind kind);
   FixedTypedArrayBase* EmptyFixedTypedArrayForMap(Map* map);
 
   void RegisterStrongRoots(Object** start, Object** end);
@@ skipping 1642 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_