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

runtime/vm/scanner.cc

Index: runtime/vm/scanner.cc
diff --git a/runtime/vm/scanner.cc b/runtime/vm/scanner.cc
index 9cbe84a220997bba73911bebd9b281cffb478a72..19509b5188b1917121ae9595b91f920ab4c46813 100644
--- a/runtime/vm/scanner.cc
+++ b/runtime/vm/scanner.cc
@@ -329,11 +329,13 @@ void Scanner::ScanIdentChars(bool allow_dollar) {
 
   // 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;
 }