Make assertion scopes thread safe.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3135 matching lines @@
             bool is_internalized_string,
             bool is_not_in_new_space,
             bool boolean_value);
 
   Handle<Object> handle() {
     if (handle_.is_null()) {
       // Default arguments to is_not_in_new_space depend on this heap number
       // to be tenured so that it's guaranteed not be be located in new space.
       handle_ = FACTORY->NewNumber(double_value_, TENURED);
     }
-    ALLOW_HANDLE_DEREF(Isolate::Current(), "smi check");
+    AllowDeferredHandleDereference smi_check;
     ASSERT(has_int32_value_ || !handle_->IsSmi());
     return handle_;
   }
 
   bool IsSpecialDouble() const {
     return has_double_value_ &&
         (BitCast<int64_t>(double_value_) == BitCast<int64_t>(-0.0) ||
          FixedDoubleArray::is_the_hole_nan(double_value_) ||
          std::isnan(double_value_));
   }
@@ skipping 3333 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_