dart2dart: Fix fallthrough in while statements.

sdk/lib/_internal/compiler/implementation/dart_backend/dart_codegen.dart

 // Copyright (c) 2014, 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 dart_codegen;
 
 import 'dart_tree.dart' as tree;
 import 'dart_printer.dart';
 import 'dart_tree_printer.dart' show TreePrinter;
 import '../tree/tree.dart' as frontend;
@@ skipping 172 matching lines @@
     visitStatement(stmt.elseStatement);
     savedBuffer.add(
         new If(condition, new Block(thenBuffer), new Block(elseBuffer)));
     statementBuffer = savedBuffer;
   }
 
   void visitWhile(tree.While stmt) {
     Expression condition = new Literal(new dart2js.BoolConstant(true));
     List<Statement> savedBuffer = statementBuffer;
     statementBuffer = <Statement>[];
+    tree.Statement savedFallthrough = fallthrough;
+    fallthrough = stmt.body;
     visitStatement(stmt.body);
     savedBuffer.add(
         new LabeledStatement(
             stmt.label.name,
             new While(condition, new Block(statementBuffer))));
     statementBuffer = savedBuffer;
+    fallthrough = savedFallthrough;
   }
 
   Expression visitConstant(tree.Constant exp) {
     return emitConstant(exp.value);
   }
 
   Expression visitLiteralList(tree.LiteralList exp) {
     return new LiteralList(
         exp.values.map(visitExpression).toList(growable: false));
   }
@@ skipping 142 matching lines @@
             emitConstant(constant.keys.entries[i]),
             emitConstant(constant.values[i])));
       }
       return new LiteralMap(entries, isConst: true);
     } else {
       throw "Unsupported constant: $constant";
     }
   }
 }