Remove support for SDK dependencies.

utils/pub/sdk_source.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 sdk_source;
-
-import 'dart:async';
-
-import '../../pkg/pathos/lib/path.dart' as path;
-
-import 'io.dart';
-import 'package.dart';
-import 'pubspec.dart';
-import 'sdk.dart' as sdk;
-import 'source.dart';
-import 'utils.dart';
-import 'version.dart';
-
-/// A package source that uses libraries from the Dart SDK.
-class SdkSource extends Source {
-  final String name = "sdk";
-  final bool shouldCache = false;
-
-  /// SDK packages are not individually versioned. Instead, their version is
-  /// inferred from the revision number of the SDK itself.
-  Future<Pubspec> describe(PackageId id) {
-    return defer(() {
-      var packageDir = _getPackagePath(id);
-      // TODO(rnystrom): What if packageDir is null?
-      var pubspec = new Pubspec.load(id.name, packageDir, systemCache.sources);
-      // Ignore the pubspec's version, and use the SDK's.
-      return new Pubspec(id.name, sdk.version, pubspec.dependencies,
-          pubspec.devDependencies, pubspec.environment);
-    });
-  }
-
-  /// Since all the SDK files are already available locally, installation just
-  /// involves symlinking the SDK library into the packages directory.
-  Future<bool> install(PackageId id, String destPath) {
-    return defer(() {
-      var path = _getPackagePath(id);
-      if (path == null) return false;
-
-      return createPackageSymlink(id.name, path, destPath).then((_) => true);
-    });
-  }
-
-  /// Gets the path in the SDK's "pkg" directory to the directory containing
-  /// package [id]. Returns `null` if the package could not be found.
-  String _getPackagePath(PackageId id) {
-    var pkgPath = path.join(sdk.rootDirectory, "pkg", id.description);
-    return dirExists(pkgPath) ? pkgPath : null;
-  }
-}