Add Map.unmodifiable constructor.

runtime/lib/integers_patch.dart

 // 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.
 // Dart core library.
 
 // VM implementation of int.
 
 patch class int {
 
   /* patch */ const factory int.fromEnvironment(String name,
@@ skipping 153 matching lines @@
           if (digit < 10 || digit >= radix) return null;
         }
         result = radix * result + digit;
       }
     }
     return result;
   }
 
   // For each radix, 2-36, how many digits are guaranteed to fit in a smi,
   // and magnitude of such a block (radix ** digit-count).
-  // 32-bit limit/multiplier at (radix - 2)*4, 64-bit limit at (radix-2)*4+1
+  // 32-bit limit/multiplier at (radix - 2)*4, 64-bit limit at (radix-2)*4+2
   static const _PARSE_LIMITS = const [
     30, 1073741824,  62, 4611686018427387904,  /* radix: 2 */
     18,  387420489,  39, 4052555153018976267,
     15, 1073741824,  30, 1152921504606846976,
     12,  244140625,  26, 1490116119384765625,  /* radix: 5 */
     11,  362797056,  23,  789730223053602816,
     10,  282475249,  22, 3909821048582988049,
     10, 1073741824,  20, 1152921504606846976,
      9,  387420489,  19, 1350851717672992089,
      9, 1000000000,  18, 1000000000000000000,  /* radix: 10 */
@@ skipping 18 matching lines @@
      6,  594823321,  12,  353814783205469041,
      6,  729000000,  12,  531441000000000000,  /* radix: 30 */
      6,  887503681,  12,  787662783788549761,
      6, 1073741824,  12, 1152921504606846976,
      5,   39135393,  12, 1667889514952984961,
      5,   45435424,  12, 2386420683693101056,
      5,   52521875,  12, 3379220508056640625,  /* radix: 35 */
      5,   60466176,  11,  131621703842267136,
   ];
 }