Use helper methods for running pub.

sdk/lib/_internal/pub/lib/src/package.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 package;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
 import 'io.dart';
 import 'pubspec.dart';
 import 'source_registry.dart';
+import 'utils.dart';
 import 'version.dart';
 
 final _README_REGEXP = new RegExp(r"^README($|\.)", caseSensitive: false);
 
 /// A named, versioned, unit of code and resource reuse.
 class Package {
   /// The path to the directory containing the package.
   final String dir;
 
   /// The name of the package.
@@ skipping 159 matching lines @@
   bool operator ==(other) {
     // TODO(rnystrom): We're assuming here that we don't need to delve into the
     // description.
     return other is PackageDep &&
            other.name == name &&
            other.source == source &&
            other.constraint == constraint;
   }
 }
 
-class PubspecNotFoundException implements Exception {
+class PubspecNotFoundException extends ApplicationException {
   final String name;
 
-  PubspecNotFoundException(this.name);
-
-  String toString() => 'Package "$name" doesn\'t have a pubspec.yaml file.';
+  PubspecNotFoundException(String name)
+      : name = name,
+        super('Package "$name" doesn\'t have a pubspec.yaml file.');
 }
 
-class PubspecHasNoNameException implements Exception {
+class PubspecHasNoNameException extends ApplicationException {
   final String name;
 
-  PubspecHasNoNameException(this.name);
-
-  String toString() => 'Package "$name"\'s pubspec.yaml file is missing the '
-    'required "name" field (e.g. "name: $name").';
+  PubspecHasNoNameException(String name)
+      : name = name,
+        super('Package "$name"\'s pubspec.yaml file is missing the '
+              'required "name" field (e.g. "name: $name").');
 }
 
-class PubspecNameMismatchException implements Exception {
+class PubspecNameMismatchException extends ApplicationException {
   final String expectedName;
   final String actualName;
 
-  PubspecNameMismatchException(this.expectedName, this.actualName);
-
-  String toString() => 'The name you specified for your dependency, '
-    '"$expectedName", doesn\'t match the name "$actualName" in its pubspec.';
+  PubspecNameMismatchException(String expectedName, String actualName)
+      : expectedName = expectedName,
+        actualName = actualName,
+        super('The name you specified for your dependency, "$expectedName", '
+              'doesn\'t match the name "$actualName" in its pubspec.');
 }