Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/kernel/kernel_enum_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.kernel_enum_builder;
 
 import 'package:kernel/ast.dart' show
     Arguments,
     AsyncMarker,
     Class,
@@ skipping 33 matching lines @@
     EnumBuilder,
     FormalParameterBuilder,
     KernelConstructorBuilder,
     KernelFieldBuilder,
     KernelFormalParameterBuilder,
     KernelInterfaceTypeBuilder,
     KernelLibraryBuilder,
     KernelProcedureBuilder,
     KernelTypeBuilder,
     LibraryBuilder,
-    MemberBuilder,
     MetadataBuilder;
 
 class KernelEnumBuilder extends SourceClassBuilder
     implements EnumBuilder<KernelTypeBuilder, InterfaceType> {
   final List<String> constants;
 
   final MapLiteral toStringMap;
 
   final KernelTypeBuilder intType;
 
@@ skipping 64 matching lines @@
           new KernelFieldBuilder(null, selfType, name, constMask | staticMask);
       members[name] = fieldBuilder;
       toStringEntries.add(new MapEntry(
               new IntLiteral(index), new StringLiteral("$className.$name")));
       index++;
     }
     MapLiteral toStringMap = new MapLiteral(toStringEntries, isConst: true);
     KernelEnumBuilder enumBuilder = new KernelEnumBuilder.internal(metadata,
         name, members, types, cls, constants, toStringMap, intType, stringType,
         parent);
-    members.forEach((String name, MemberBuilder builder) {
+    // TODO(sigmund): dynamic should be `covariant MemberBuilder`.
+    members.forEach((String name, dynamic builder) {

[ahe, 2017/02/07 11:03:08]

I think I prefer this:

members.forEach((String name, dynamic b) {
  MemberBuilder builder = b;
...
}

Two or three other places. Thank you for adding the todo.

[Siggi Cherem (dart-lang), 2017/02/07 21:59:26]

Done. I had that in on my first change and I thought you wanted me to remove it
when switching to dynamic :), just added it back.

[ahe, 2017/02/08 19:59:23]

Yeah, sorry about that. Sometimes stuffs needs to be really concrete for me to
understand the trade offs. This is part of the reason I'd preferred to do this
task myself at a later time.

[Siggi Cherem (dart-lang), 2017/02/09 04:44:02]

No problem, I understand

       builder.parent = enumBuilder;
     });
     selfType.builder = enumBuilder;
     return enumBuilder;
   }
 
   InterfaceType buildType(List<KernelTypeBuilder> arguments) {
     return cls.rawType;
   }
 
@@ skipping 32 matching lines @@
       Arguments arguments =
           new Arguments(<Expression>[new IntLiteral(index++)]);
       field.initializer =
           new ConstructorInvocation(constructor, arguments, isConst: true);
     }
     return super.build(libraryBuilder);
   }
 
   Builder findConstructorOrFactory(String name) => null;
 }