Untank compilation and fix JSON parse bug introduced in r8147.

src/json-parser.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 74 matching lines @@
       AdvanceSkipWhitespace();
       return true;
     }
     return false;
   }
 
   // A JSON string (production JSONString) is subset of valid JavaScript string
   // literals. The string must only be double-quoted (not single-quoted), and
   // the only allowed backslash-escapes are ", /, \, b, f, n, r, t and
   // four-digit hex escapes (uXXXX). Any other use of backslashes is invalid.
-  Handle<Object> ParseJsonString() {
+  Handle<String> ParseJsonString() {
     return ScanJsonString<false>();
   }
-  Handle<Object> ParseJsonSymbol() {
+  Handle<String> ParseJsonSymbol() {
     return ScanJsonString<true>();
   }
   template <bool is_symbol>
-  Handle<Object> ScanJsonString();
+  Handle<String> ScanJsonString();
   // Slow version for unicode support, uses the first ascii_count characters,
   // as first part of a ConsString
-  Handle<Object> SlowScanJsonString();
+  Handle<String> SlowScanJsonString();
 
   // A JSON number (production JSONNumber) is a subset of the valid JavaScript
   // decimal number literals.
   // It includes an optional minus sign, must have at least one
   // digit before and after a decimal point, may not have prefixed zeros (unless
   // the integer part is zero), and may include an exponent part (e.g., "e-10").
   // Hexadecimal and octal numbers are not allowed.
   Handle<Object> ParseJsonNumber();
 
   // Parse a single JSON value from input (grammar production JSONValue).
@@ skipping 41 matching lines @@
   Isolate* isolate_;
   uc32 c0_;
   int position_;
 
   double number_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_PARSER_H_