Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/source/outline_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.outline_builder;
 
 import 'package:kernel/ast.dart' show
     AsyncMarker,
     ProcedureKind;
 
@@ skipping 376 matching lines @@
     push(parameters);
   }
 
   @override
   void endFormalParameters(int count, Token beginToken, Token endToken) {
     debugEvent("FormalParameters");
     List formals = popList(count);
     if (formals != null && formals.isNotEmpty) {
       var last = formals.last;
       if (last is List) {
-        var newList =
+        // TODO(sigmund): change `List newList` back to `var` (this is a
+        // workaround for issue #28651). Eventually, make optional
+        // formals a separate stack entry (#28673).
+        List newList =
             new List<FormalParameterBuilder>(formals.length - 1 + last.length);
         newList.setRange(0, formals.length - 1, formals);
         newList.setRange(formals.length - 1, newList.length, last);
         for (int i = 0; i < last.length; i++) {
           newList[i + formals.length - 1] = last[i];
         }
         formals = newList;
       }
     }
     if (formals != null) {
@@ skipping 167 matching lines @@
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!isDartLibrary || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }