Int32 constants should be const.

pkg/fixnum/lib/src/int32.dart

Index: pkg/fixnum/lib/src/int32.dart
diff --git a/pkg/fixnum/lib/src/int32.dart b/pkg/fixnum/lib/src/int32.dart
index 1e139d2478224e407cb371b45a1fe3b1859cc2a1..520e586e666f120b65cc8ab757c9bb7e9925d83f 100644
--- a/pkg/fixnum/lib/src/int32.dart
+++ b/pkg/fixnum/lib/src/int32.dart
@@ -20,22 +20,22 @@ class Int32 implements IntX {
    * The minimum positive value attainable by an [Int32], namely
    * -2147483648.
    */
-  static Int32 MIN_VALUE = const Int32._internal(-0x80000000);
+  static const Int32 MIN_VALUE = const Int32._internal(-0x80000000);
 
   /**
    * An [Int32] constant equal to 0.
    */
-  static Int32 ZERO = const Int32._internal(0);
+  static const Int32 ZERO = const Int32._internal(0);
 
   /**
    * An [Int32] constant equal to 1.
    */
-  static Int32 ONE = const Int32._internal(1);
+  static const Int32 ONE = const Int32._internal(1);
 
   /**
    * An [Int32] constant equal to 2.
    */
-  static Int32 TWO = const Int32._internal(2);
+  static const Int32 TWO = const Int32._internal(2);
 
   // Hex digit char codes
   static const int _CC_0 = 48; // '0'.codeUnitAt(0)