pkg/compiler: fix imports

pkg/compiler/lib/src/apiimpl.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.
 
 library leg_apiimpl;
 
 import 'dart:async';
-import 'dart:convert';
 
 import 'package:package_config/packages.dart';
 import 'package:package_config/packages_file.dart' as pkgs;
 import 'package:package_config/src/packages_impl.dart'
     show MapPackages, NonFilePackagesDirectoryPackages;
 import 'package:package_config/src/util.dart' show checkValidPackageUri;
 
 import '../compiler_new.dart' as api;
 import 'common/tasks.dart' show GenericTask, Measurer;
 import 'common.dart';
-import 'common/backend_api.dart' show Backend;
 import 'compiler.dart';
 import 'diagnostics/messages.dart' show Message;
 import 'elements/elements.dart' as elements;
 import 'environment.dart';
 import 'io/source_file.dart';
 import 'options.dart' show CompilerOptions;
 import 'platform_configuration.dart' as platform_configuration;
 import 'resolved_uri_translator.dart';
 import 'script.dart';
-import 'serialization/system.dart';
 
 /// Implements the [Compiler] using a [api.CompilerInput] for supplying the
 /// sources.
 class CompilerImpl extends Compiler {
   final Measurer measurer;
   api.CompilerInput provider;
   api.CompilerDiagnostics handler;
   Packages packages;
 
   bool get mockableLibraryUsed => resolvedUriTranslator.isSet
@@ skipping 357 matching lines @@
   }
 }
 
 /// For every 'dart:' library, a corresponding environment variable is set
 /// to "true". The environment variable's name is the concatenation of
 /// this prefix and the name (without the 'dart:'.
 ///
 /// For example 'dart:html' has the environment variable 'dart.library.html' set
 /// to "true".
 const String _dartLibraryEnvironmentPrefix = 'dart.library.';