make unimplemented statements throw

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, 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 dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet;
 import 'dart:io' show Directory, File;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
@@ skipping 1636 matching lines @@
   }
 
   @override
   visitInterpolationExpression(InterpolationExpression node) =>
       _visit(node.expression);
 
   @override
   visitBooleanLiteral(BooleanLiteral node) => js.boolean(node.value);
 
   @override
-  JS.Statement visitDeclaration(Declaration node) =>
-      js.comment('Unimplemented ${node.runtimeType}: $node');
-
-  @override
-  JS.Statement visitStatement(Statement node) =>
-      js.comment('Unimplemented ${node.runtimeType}: $node');
-
-  @override
   JS.Expression visitExpression(Expression node) =>
       _unimplementedCall('Unimplemented ${node.runtimeType}: $node');
 
   JS.Expression _unimplementedCall(String comment) {
     return js.call('dart.throw_(#)', [js.escapedString(comment)]);
   }
 
   @override
   visitNode(AstNode node) {
     // TODO(jmesserly): verify this is unreachable.
@@ skipping 346 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unncessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }