Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart

Index: pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart b/pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart
index 8728eafb7ae48d744b59b6af3ff14f8f82f87887..0df0d384e5c2caa49d793605a052a39510b19bd3 100644
--- a/pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/builder_accessors.dart
@@ -10,6 +10,9 @@ export 'frontend_accessors.dart' show
 import 'frontend_accessors.dart' show
     Accessor;
 
+import 'package:meta/meta.dart' show
+    virtual;
+
 import 'package:kernel/ast.dart';
 
 import 'package:kernel/core_types.dart' show
@@ -97,7 +100,7 @@ abstract class BuilderAccessor implements Accessor {
         isSetter: true);
   }
 
-  Expression doInvocation(int charOffset, Arguments arguments);
+  doInvocation(int charOffset, Arguments arguments);

[ahe, 2017/02/02 07:28:30]

Please don't remove explicit types.

[Siggi Cherem (dart-lang), 2017/02/02 16:30:35]

There is a subclass that returns a non-expression here

[Siggi Cherem (dart-lang), 2017/02/06 23:35:50]

To be specific `ThisAccessor` might return an Initializer. Let me know if you'd
like me to add a dartdoc about it here.

 
   buildPropertyAccess(IncompleteSend send, bool isNullAware) {
     if (send is SendAccessor) {
@@ -287,7 +290,7 @@ abstract class IncompleteSend extends BuilderAccessor {
 
   final int charOffset;
 
-  final Name name;
+  @virtual final Name name;
 
   IncompleteSend(this.helper, this.charOffset, this.name);