Change sort on scalar arrays to take optional comparison function.

runtime/lib/byte_array.dart

Index: runtime/lib/byte_array.dart
diff --git a/runtime/lib/byte_array.dart b/runtime/lib/byte_array.dart
index feadf0e90a7024149f784b45fd33613a80d91da2..dd953f3cc52b5638d34fe4a21e32462487a5d31c 100644
--- a/runtime/lib/byte_array.dart
+++ b/runtime/lib/byte_array.dart
@@ -181,7 +181,7 @@ abstract class _ByteArrayBase {
         "Cannot add to a non-extendable array");
   }
 
-  void sort(int compare(a, b)) {
+  void sort([Comparator compare = Comparable.compare]) {
     DualPivotQuicksort.sort(this, compare);
   }
 
@@ -1659,7 +1659,7 @@ class _ByteArrayViewBase {
         "Cannot add to a non-extendable array");
   }
 
-  void sort(int compare(a, b)) {
+  void sort([Comparator compare = Comparable.compare]) {
     DualPivotQuicksort.sort(this, compare);
   }