Add a safe API for creating ASCII-only strings

src/factory.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 99 matching lines @@
   //   - ...FromTwoByte initializes the string from a buffer that is two
   //     byte encoded.  If the characters are all single-byte characters,
   //     the result will be converted to ASCII, otherwise it will be left as
   //     two byte.
   //
   // ASCII strings are pretenured when used as keys in the SourceCodeCache.
   Handle<String> NewStringFromAscii(
       Vector<const char> str,
       PretenureFlag pretenure = NOT_TENURED);
 
+  Handle<String> NewStringFromAsciiSafe(
+      Vector<const char> str,
+      PretenureFlag pretenure = NOT_TENURED);
+
   // UTF8 strings are pretenured when used for regexp literal patterns and
   // flags in the parser.
   Handle<String> NewStringFromUtf8(
       Vector<const char> str,
       PretenureFlag pretenure = NOT_TENURED);
 
   Handle<String> NewStringFromTwoByte(
       Vector<const uc16> str,
       PretenureFlag pretenure = NOT_TENURED);
 
@@ skipping 382 matching lines @@
   // Update the map cache in the native context with (keys, map)
   Handle<MapCache> AddToMapCache(Handle<Context> context,
                                  Handle<FixedArray> keys,
                                  Handle<Map> map);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_