Calculate string hash during flattening.

src/heap.h

 // Copyright 2006-2008 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 510 matching lines @@
   // Finds the symbol for string in the symbol table.
   // If not found, a new symbol is added to the table and returned.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if allocation
   // failed.
   // Please note this function does not perform a garbage collection.
   static Object* LookupSymbol(Vector<const char> str);
   static Object* LookupAsciiSymbol(const char* str) {
     return LookupSymbol(CStrVector(str));
   }
   static Object* LookupSymbol(String* str);
+  static bool LookupSymbolIfExists(String* str, String** symbol);
 
   // Compute the matching symbol map for a string if possible.
   // NULL is returned if string is in new space or not flattened.
   static Map* SymbolMapForString(String* str);
 
   // Converts the given boolean condition to JavaScript boolean value.
   static Object* ToBoolean(bool condition) {
     return condition ? true_value() : false_value();
   }
 
@@ skipping 621 matching lines @@
   int marked_count_;
 
   // The count from the end of the previous full GC.  Will be zero if there
   // was no previous full GC.
   int previous_marked_count_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_