Sped up hashCode by removing megamorphic call to _identityHashCode.

runtime/lib/bigint.dart

 // Copyright (c) 2014, 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.
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 /*
  * Copyright (c) 2003-2005  Tom Wu
@@ skipping 1188 matching lines @@
     }
     // Return remainder, i.e. denormalized r_digits[0..y_used-1].
     r_used = y_used;
     if (nsh > 0) {
       // Denormalize remainder.
       r_used = _rShiftDigits(r_digits, r_used, nsh, r_digits);
     }
     return r_used;
   }
 
-  int get _identityHashCode {
-    return this;
-  }
+  int get hashCode => this;
+  int get _identityHashCode => this;
+
   int operator ~() {
     return _not()._toValidInt();
   }
 
   int get bitLength {
     if (_used == 0) return 0;
     if (_neg) return (~this).bitLength;
     return _DIGIT_BITS*(_used - 1) + _nbits(_digits[_used - 1]);
   }
 
@@ skipping 860 matching lines @@
 
   int _mul(Uint32List x_digits, int x_used,
            Uint32List y_digits, int y_used,
            Uint32List r_digits) {
     var r_used = _Bigint._mulDigits(x_digits, x_used,
                                     y_digits, y_used,
                                     r_digits);
     return _reduce(r_digits, r_used);
   }
 }