Port patch 8847 to the 3.4 branch.

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 439 matching lines @@
   int count = end - start;
   int max_length = count + source_length_ - position_;
   int length = Min(max_length, Max(kInitialSpecialStringLength, 2 * count));
   Handle<StringType> seq_str = NewRawString<StringType>(isolate()->factory(),
                                                         length);
   // Copy prefix into seq_str.
   SinkChar* dest = seq_str->GetChars();
   String::WriteToFlat(*prefix, dest, start, end);
 
   while (c0_ != '"') {
+    // Check for control character (0x00-0x1f) or unterminated string (<0).
+    if (c0_ < 0x20) return Handle<String>::null();
     if (count >= length) {
       // We need to create a longer sequential string for the result.
       return SlowScanJsonString<StringType, SinkChar>(seq_str, 0, count);
     }
-    // Check for control character (0x00-0x1f) or unterminated string (<0).
-    if (c0_ < 0x20) return Handle<String>::null();
     if (c0_ != '\\') {
       // If the sink can contain UC16 characters, or source_ contains only
       // ASCII characters, there's no need to test whether we can store the
       // character. Otherwise check whether the UC16 source character can fit
       // in the ASCII sink.
       if (sizeof(SinkChar) == kUC16Size ||
           seq_ascii ||
           c0_ <= kMaxAsciiCharCode) {
         SeqStringSet(seq_str, count++, c0_);
         Advance();
@@ skipping 113 matching lines @@
   }
   ASSERT_EQ('"', c0_);
   // Advance past the last '"'.
   AdvanceSkipWhitespace();
   return result;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_PARSER_H_