Have dartdevc support --version.

pkg/dev_compiler/web/web_command.dart

 // Copyright (c) 2016, 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.
 @JS()
 library dev_compiler.web.web_command;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:html' show HttpRequest;
 
 import 'package:analyzer/dart/element/element.dart'
     show
         LibraryElement,
         ImportElement,
         ShowElementCombinator,
         HideElementCombinator;
 import 'package:analyzer/file_system/file_system.dart' show ResourceUriResolver;
 import 'package:analyzer/file_system/memory_file_system.dart'
     show MemoryResourceProvider;
 import 'package:analyzer/src/context/context.dart' show AnalysisContextImpl;
 import 'package:analyzer/src/summary/idl.dart' show PackageBundle;
 import 'package:analyzer/src/summary/package_bundle_reader.dart'
     show
         SummaryDataStore,
         InSummaryUriResolver,
-        InputPackagesResultProvider,
         InSummarySource;
 import 'package:analyzer/src/dart/resolver/scope.dart' show Scope;
 
 import 'package:args/command_runner.dart';
 
 import 'package:dev_compiler/src/analyzer/context.dart' show AnalyzerOptions;
 import 'package:dev_compiler/src/compiler/compiler.dart'
     show BuildUnit, CompilerOptions, JSModuleFile, ModuleCompiler;
 
 import 'package:dev_compiler/src/compiler/module_builder.dart';
@@ skipping 244 matching lines @@
   if (source is InSummarySource) {
     return source.summaryPath.substring(1).replaceAll('.api.ds', '');
   }
   return source.toString().substring(1).replaceAll('.dart', '');
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }