Improve keyed loads on strings by using a new stub

src/runtime.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 128 matching lines @@
   F(Math_sin, 1, 1) \
   F(Math_sqrt, 1, 1) \
   F(Math_tan, 1, 1) \
   \
   /* Regular expressions */ \
   F(RegExpCompile, 3, 1) \
   F(RegExpExec, 4, 1) \
   \
   /* Strings */ \
   F(StringCharCodeAt, 2, 1) \
+  F(StringCharAt, 2, 1) \
   F(StringIndexOf, 3, 1) \
   F(StringLastIndexOf, 3, 1) \
   F(StringLocaleCompare, 2, 1) \
   F(SubString, 3, 1) \
   F(StringReplaceRegExpWithString, 4, 1) \
   F(StringMatch, 3, 1) \
   F(StringTrim, 3, 1) \
   \
   /* Numbers */ \
   F(NumberToRadixString, 2, 1) \
@@ skipping 261 matching lines @@
                                                 int position);
 
   // Helper functions used stubs.
   static void PerformGC(Object* result);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_