remove dependencies to analyzer from lib/src/fasta

pkg/front_end/lib/src/fasta/environment_variable.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.
-
-library fasta.environment_variable;
-
-import 'dart:async' show Future;
-
-import 'dart:io' show Directory, File, Platform;
-
-import 'errors.dart' show inputError;
-
-class EnvironmentVariable {
-  final String name;
-
-  final String what;
-
-  const EnvironmentVariable(this.name, this.what);
-
-  Future<String> get value async {
-    String value = Platform.environment[name];
-    if (value == null) return variableNotDefined();
-    await validate(value);
-    return value;
-  }
-
-  Future<Null> validate(String value) => new Future<Null>.value();
-
-  variableNotDefined() {
-    inputError(
-        null, null, "The environment variable '$name' isn't defined. $what");
-  }
-}
-
-class EnvironmentVariableFile extends EnvironmentVariable {
-  const EnvironmentVariableFile(String name, String what) : super(name, what);
-
-  Future<Null> validate(String value) async {
-    if (!await new File(value).exists()) notFound(value);
-    return null;
-  }
-
-  notFound(String value) {
-    inputError(
-        null,
-        null,
-        "The environment variable '$name' has the value "
-        "'$value', that isn't a file. $what");
-  }
-}
-
-class EnvironmentVariableDirectory extends EnvironmentVariable {
-  const EnvironmentVariableDirectory(String name, String what)
-      : super(name, what);
-
-  Future<Null> validate(String value) async {
-    if (!await new Directory(value).exists()) notFound(value);
-    return null;
-  }
-
-  notFound(String value) {
-    inputError(
-        null,
-        null,
-        "The environment variable '$name' has the value "
-        "'$value', that isn't a directory. $what");
-  }
-}
-
-Future<bool> fileExists(Uri base, String path) async {
-  return await new File.fromUri(base.resolve(path)).exists();
-}