Merge kernel closure conversion into the Dart SDK

pkg/kernel/test/uint31_pair_map_bench.dart

 import 'package:kernel/type_propagation/canonicalizer.dart';
 
 main() {
   Stopwatch watch = new Stopwatch()..start();
 
   const int lowBiasKeys = 100;
   const int highBiasKeys = 10000;
   const int noBiasKeys = 1000;
 
   Uint31PairMap map;
@@ skipping 40 matching lines @@
   }
   int rightBiasTime = watch.elapsedMicroseconds;
 
   print('''
 bias.none:  ${formatTime(noBiasTime)}
 bias.left:  ${formatTime(leftBiasTime)}
 bias.right: ${formatTime(rightBiasTime)}
 ''');
 }
 
-
 String formatTime(int microseconds) {
   double seconds = microseconds / 1000000.0;
   return '$seconds s';
 }