Implement correct scoping rules for variables.

sdk/lib/_internal/compiler/implementation/dart_backend/backend.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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 94 matching lines @@
       return statement;
     }
 
     NodeList statements = block.statements;
     LinkBuilder<Statement> builder = new LinkBuilder<Statement>();
     for (Statement statement in statements.nodes) {
       if (!shouldOmit(statement)) {
         builder.addLast(visit(rewriteStatement(statement)));
       }
     }
-    return new Block(rewriteNodeList(statements, builder.toLink()));
+    return new Block(rewriteNodeList(statements, builder.toLink()),
+                     block.declarations);
   }
 }
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
   final bool forceStripTypes;
   final bool stripAsserts;
   // TODO(antonm): make available from command-line options.
   final bool outputAst = false;
   final Map<Node, String> renames;
@@ skipping 502 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().canonicalUri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Iterable<Element> elements) =>
     sorted(elements, compareElements);