pkg/analyzer: support latest pkg/crypto version

pkg/analyzer/lib/src/summary/summarize_elements.dart

Index: pkg/analyzer/lib/src/summary/summarize_elements.dart
diff --git a/pkg/analyzer/lib/src/summary/summarize_elements.dart b/pkg/analyzer/lib/src/summary/summarize_elements.dart
index bb2a42e23ed15e295a5a8c27fd074bf42cdb80a1..74e10f018a96b214834ecb576ec3c1d33874a773 100644
--- a/pkg/analyzer/lib/src/summary/summarize_elements.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_elements.dart
@@ -19,6 +19,7 @@ import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/name_filter.dart';
 import 'package:analyzer/src/summary/summarize_const_expr.dart';
+import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:path/path.dart' as path;
 
@@ -212,9 +213,7 @@ class PackageBundleAssembler {
    * Compute a hash of the given file contents.
    */
   String _hash(String contents) {
-    MD5 md5 = new MD5();
-    md5.add(UTF8.encode(contents));
-    return CryptoUtils.bytesToHex(md5.close());
+    return hex.encode(md5.convert(UTF8.encode(contents)).bytes);
   }
 }