Address issues found with analyzer

dart/site/try/src/caching_compiler.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.
 
 library trydart.caching_compiler;
 
 import 'dart:profiler' show
     UserTag;
 
 import 'package:compiler/compiler.dart' show
     CompilerInputProvider,
     CompilerOutputProvider,
     Diagnostic,
     DiagnosticHandler;
 
 import 'package:compiler/implementation/apiimpl.dart' show
     Compiler;
 
 import 'package:compiler/implementation/dart2jslib.dart' show
     LibraryLoaderTask, // TODO(ahe): Remove this import.
     NullSink;
 
 import 'package:compiler/implementation/js_backend/js_backend.dart' show
     JavaScriptBackend;
 
 import 'package:compiler/implementation/elements/elements.dart' show
     LibraryElement;
 
-import 'package:compiler/implementation/native_handler.dart' as native;
-
 void clearLibraryLoader(LibraryLoaderTask libraryLoader) {
   // TODO(ahe): Move this method to [LibraryLoader].
   libraryLoader
       ..libraryResourceUriMap.clear()
       ..libraryNames.clear();
 }
 
 void reuseLibrary(
     LibraryLoaderTask libraryLoader,
     LibraryElement library) {
@@ skipping 131 matching lines @@
       if (library.isPlatformLibrary ||
           (packagesAreImmutable && library.isPackageLibrary)) {
         compiler.libraries[uri] = library;
         reuseLibrary(compiler.libraryLoader, library);
       }
     });
   }
   oldTag.makeCurrent();
   return compiler;
 }