Cleanup some ambiguous and incorrect types and disable a case that in analyzer.dart that seems like…

lib/visitor.dart

 // Copyright (c) 2012, 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 csslib.visitor;
 
 import 'package:source_span/source_span.dart';
 import 'parser.dart';
 
 part 'src/css_printer.dart';
@@ skipping 22 matching lines @@
   void visitNamespaceDirective(NamespaceDirective node);
   void visitVarDefinitionDirective(VarDefinitionDirective node);
   void visitMixinDefinition(MixinDefinition node);
   void visitMixinRulesetDirective(MixinRulesetDirective node);
   void visitMixinDeclarationDirective(MixinDeclarationDirective node);
   void visitIncludeDirective(IncludeDirective node);
   void visitContentDirective(ContentDirective node);
 
   void visitRuleSet(RuleSet node);
   void visitDeclarationGroup(DeclarationGroup node);
-  void visitMarginGroup(DeclarationGroup node);
+  void visitMarginGroup(MarginGroup node);
   void visitDeclaration(Declaration node);
   void visitVarDefinition(VarDefinition node);
   void visitIncludeMixinAtDeclaration(IncludeMixinAtDeclaration node);
   void visitExtendDeclaration(ExtendDeclaration node);
   void visitSelectorGroup(SelectorGroup node);
   void visitSelector(Selector node);
   void visitSimpleSelectorSequence(SimpleSelectorSequence node);
   void visitSimpleSelector(SimpleSelector node);
   void visitElementSelector(ElementSelector node);
   void visitNamespaceSelector(NamespaceSelector node);
@@ skipping 392 matching lines @@
   void visitPaddingExpression(PaddingExpression node) {
     // TODO(terry): TBD
     throw UnimplementedError;
   }
 
   void visitWidthExpression(WidthExpression node) {
     // TODO(terry): TBD
     throw UnimplementedError;
   }
 }