Change new List(n) to return fixed length list.

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 c7804c20623600810ad6fd7a4bc3d1a0fea719f3..02eb2139b46dc0c1d981364027b3873d97b18f10 100644
--- a/pkg/fixnum/lib/src/int32.dart
+++ b/pkg/fixnum/lib/src/int32.dart
@@ -288,7 +288,7 @@ class int32 implements intx {
     return _i == _convert(other);
   }
 
-  int compareTo(other) {
+  int compareTo(Comparable other) {
     if (other is int64) {
       return this.toInt64().compareTo(other);
     }
@@ -338,7 +338,7 @@ class int32 implements intx {
   int numberOfTrailingZeros() => _numberOfTrailingZeros(_i);
 
   List<int> toBytes() {
-    List<int> result = new List<int>.fixedLength(4);
+    List<int> result = new List<int>(4);
     result[0] = _i & 0xff;
     result[1] = (_i >> 8) & 0xff;
     result[2] = (_i >> 16) & 0xff;