Do not add a private identifier twice into the symbol table, once without the private key appended …

runtime/vm/scanner.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/scanner.h"
 
 #include "platform/assert.h"
 #include "vm/dart.h"
 #include "vm/flags.h"
 #include "vm/object.h"
@@ skipping 311 matching lines @@
           current_token_.kind = keywords_[i].kind;
           return;
         }
       }
       i++;
     }
   }
 
   // We did not read a keyword.
   current_token_.kind = Token::kIDENT;
-  String& literal =
-      String::ZoneHandle(Z, Symbols::New(T, source_, ident_pos, ident_length));
+  String& literal = String::ZoneHandle(Z);
   if (ident_char0 == Library::kPrivateIdentifierStart) {
     // Private identifiers are mangled on a per library basis.
+    literal = String::SubString(source_, ident_pos, ident_length);
     literal = Symbols::FromConcat(T, literal, private_key_);
+  } else {
+    literal = Symbols::New(T, source_, ident_pos, ident_length);
   }
   current_token_.literal = &literal;
 }
 
 
 // Parse integer or double number literal of format:
 // NUMBER = INTEGER | DOUBLE
 // INTEGER = D+ | (("0x" | "0X") H+)
 // DOUBLE = ((D+ ["." D*]) | ("." D+)) [ EXPONENT ]
 // EXPONENT = ("e" | "E") ["+" | "-"] D+
@@ skipping 629 matching lines @@
     keywords_[i].keyword_symbol = &Symbols::Token(token);
 
     int ch = keywords_[i].keyword_chars[0] - 'a';
     if (keywords_char_offset_[ch] == Token::kNumKeywords) {
       keywords_char_offset_[ch] = i;
     }
   }
 }
 
 }  // namespace dart