Create stand-alone json parser (including scanner).

src/heap.h

Index: src/heap.h
===================================================================
--- src/heap.h	(revision 7898)
+++ src/heap.h	(working copy)
@@ -809,6 +809,10 @@
     return LookupSymbol(CStrVector(str));
   }
   MUST_USE_RESULT MaybeObject* LookupSymbol(String* str);
+  MUST_USE_RESULT MaybeObject* LookupAsciiSymbol(Handle<SeqAsciiString> string,
+                                                 int from,
+                                                 int length);
+
   bool LookupSymbolIfExists(String* str, String** symbol);
   bool LookupTwoCharsSymbolIfExists(String* str, String** symbol);