Make assertion scopes thread safe.

src/v8conversions.h

 // Copyright 2011 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 40 matching lines @@
                       String* str,
                       int flags,
                       double empty_string_val = 0);
 
 // Converts a string into an integer.
 double StringToInt(UnicodeCache* unicode_cache, String* str, int radix);
 
 // Converts a number into size_t.
 inline size_t NumberToSize(Isolate* isolate,
                            Object* number) {
-  NoHandleAllocation hc(isolate);
+  DisallowHandleAllocation no_handles;
   if (number->IsSmi()) {
     return Smi::cast(number)->value();
   } else {
     ASSERT(number->IsHeapNumber());
     double value = HeapNumber::cast(number)->value();
     return static_cast<size_t>(value);
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8CONVERSIONS_H_