[dart2dart] In renamer only add import prefix for top-level elements.

tests/compiler/dart2js/unparser_test.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.
 
 #import('dart:uri');
 #import('parser_helper.dart');
 #import('mock_compiler.dart');
 #import("../../../lib/compiler/compiler.dart");
 #import("../../../lib/compiler/implementation/dart_backend/dart_backend.dart");
 #import("../../../lib/compiler/implementation/elements/elements.dart");
@@ skipping 21 matching lines @@
 interface List {}
 interface Closure {}
 interface Dynamic {}
 interface Null {}
 assert() {}
 class Math {
   static double parseDouble(String s) => 1.0;
 }
 ''';
 
+final ioLib = @'''
+#library('io');
+class Platform {
+  static int operatingSystem;
+}
+''';
+
 testDart2Dart(String src, [void continuation(String s)]) {
   // If continuation is not provided, check that source string remains the same.
   if (continuation === null) {
     continuation = (s) { Expect.equals(src, s); };
   }
   testDart2DartWithLibrary(src, '', continuation);
 }
 
 /**
  * Library name is assumed to be 'mylib' in 'mylib.dart' file.
  */
 testDart2DartWithLibrary(
     String srcMain, String srcLibrary, [void continuation(String s)]) {
   fileUri(path) => new Uri.fromComponents(scheme: 'file', path: path);
 
   final scriptUri = fileUri('script.dart');
   final libUri = fileUri('mylib.dart');
 
   provider(uri) {
     if (uri == scriptUri) return new Future.immediate(srcMain);
     if (uri.toString() == libUri.toString()) {
       return new Future.immediate(srcLibrary);
     }
     if (uri.path.endsWith('/core.dart')) return new Future.immediate(coreLib);
+    if (uri.path.endsWith('/io.dart')) return new Future.immediate(ioLib);
     return new Future.immediate('');
   }
 
   handler(uri, begin, end, message, kind) {
     if (kind === Diagnostic.ERROR || kind === Diagnostic.CRASH) {
       Expect.fail('$uri: $begin-$end: $message [$kind]');
     }
   }
 
   compile(
@@ skipping 547 matching lines @@
 }
 ''';
   var expectedResult =
     'class C<T>{factory I(){}}'
     'interface I<T> default C<T>{I();}'
     'main(){new I();}';
   testDart2DartWithLibrary(mainSrc, librarySrc,
       (String result) { Expect.equals(expectedResult, result); });
 }
 
+testStaticAccessIoLib() {
+  var src = '''
+#import('dart:io');
+
+main() {
+  Platform.operatingSystem;
+}
+''';
+  var expectedResult = '#import("dart:io", prefix: "p");'
+      'main(){p.Platform.operatingSystem;}';
+  testDart2Dart(src,
+      (String result) { Expect.equals(expectedResult, result); });
+}
+
 main() {
   testSignedConstants();
   testGenericTypes();
   testForLoop();
   testEmptyList();
   testClosure();
   testIndexedOperatorDecl();
   testNativeMethods();
   testPrefixIncrements();
   testConstModifier();
@@ skipping 15 matching lines @@
   testClassExtendsWithArgs();
   testStaticInvocation();
   testLibraryGetSet();
   testFieldTypeOutput();
   testDefaultClassNamePlaceholder();
   testFactoryRename();
   testTypeVariablesAreRenamed();
   testClassTypeArgumentBound();
   testDoubleMains();
   testInterfaceDefaultAnotherLib();
+  testStaticAccessIoLib();
 }