Fix compiler stats

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 367 matching lines @@
         ErrorMsg("missing exponent digits");
         return;
       }
       while (IsDecimalDigit(c0_)) {
         ReadChar();
       }
     }
   }
   if (current_token_.kind != Token::kILLEGAL) {
     intptr_t len = lookahead_pos_ - token_start_;
-    String& str = String::ZoneHandle(Z,
-        String::SubString(source_, token_start_, len, Heap::kOld));
-    str = Symbols::New(str);
+    const String& str =
+        String::ZoneHandle(Z, Symbols::New(source_, token_start_, len));
     current_token_.literal = &str;
   }
 }
 
 
 void Scanner::SkipLine() {
   while (c0_ != '\n' && c0_ != '\0') {
     ReadChar();
   }
 }
@@ skipping 571 matching lines @@
     keywords_[i].keyword_symbol = &Symbols::Keyword(token);
 
     int ch = keywords_[i].keyword_chars[0] - 'a';
     if (keywords_char_offset_[ch] == Token::kNumKeywords) {
       keywords_char_offset_[ch] = i;
     }
   }
 }
 
 }  // namespace dart