Remove warnings from dart2js test-suite.

tests/compiler/dart2js/mirror_helper_test.dart

 // Copyright (c) 2013, 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.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import 'memory_compiler.dart' show compilerFor;
 import '../../../sdk/lib/_internal/compiler/implementation/apiimpl.dart' show
     Compiler;
 import
     '../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart'
 show
     Element, LibraryElement, ClassElement;
 import
     '../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart'
 show
-    Node;
+    Block, ExpressionStatement, FunctionExpression, Node, Send;
 import
     '../../../sdk/lib/_internal/compiler/implementation/dart_backend/dart_backend.dart'
 show
     DartBackend, ElementAst;
 import
     '../../../sdk/lib/_internal/compiler/implementation/mirror_renamer/mirror_renamer.dart'
 show
     MirrorRenamer;
 
 
@@ skipping 18 matching lines @@
 
 void testWithMirrorRenaming({bool minify}) {
   asyncTest(() => runCompiler(useMirrorHelperLibrary: true, minify: minify).
       then((Compiler compiler) {
 
     DartBackend backend = compiler.backend;
     MirrorRenamer mirrorRenamer = backend.mirrorRenamer;
     Map<Node, String> renames = backend.renames;
     Map<LibraryElement, String> imports = backend.imports;
 
-    Node getNameFunctionNode =
-        backend.memberNodes.values.first.first.body.statements.nodes.head;
+    FunctionExpression node = backend.memberNodes.values.first.first;
+    Block block = node.body;
+    ExpressionStatement getNameFunctionNode = block.statements.nodes.head;
+    Send send = getNameFunctionNode.expression;
 
     Expect.equals(renames[mirrorRenamer.mirrorHelperGetNameFunctionNode.name],
-                  renames[getNameFunctionNode.expression.selector]);
+                  renames[send.selector]);
     Expect.equals("",
-                  renames[getNameFunctionNode.expression.receiver]);
+                  renames[send.receiver]);
     Expect.equals(1, imports.keys.length);
   }));
 }
 
 void testWithoutMirrorRenaming({bool minify}) {
   asyncTest(() => runCompiler(useMirrorHelperLibrary: false, minify: minify).
       then((Compiler compiler) {
 
     DartBackend backend = compiler.backend;
     Map<Node, String> renames = backend.renames;
     Map<LibraryElement, String> imports = backend.imports;
 
-    Node getNameFunctionNode =
-        backend.memberNodes.values.first.first.body.statements.nodes.head;
+    FunctionExpression node = backend.memberNodes.values.first.first;
+    Block block = node.body;
+    ExpressionStatement getNameFunctionNode = block.statements.nodes.head;
+    Send send = getNameFunctionNode.expression;
 
-    Expect.isFalse(renames.containsKey(getNameFunctionNode.expression.selector));
-    Expect.isFalse(renames.containsKey(getNameFunctionNode.expression.receiver));
+    Expect.isFalse(renames.containsKey(send.selector));
+    Expect.isFalse(renames.containsKey(send.receiver));
     Expect.equals(1, imports.keys.length);
   }));
 }
 
 const MEMORY_SOURCE_FILES = const <String, String> {
   'main.dart': """
 import 'dart:mirrors';
 
 class Foo {
   noSuchMethod(Invocation invocation) {
     MirrorSystem.getName(invocation.memberName);
   }
 }
 
 void main() {
   new Foo().fisk();
 }
 """};