Rename several classes in barback.

pkg/barback/lib/src/asset_provider.dart

-// Copyright (c) 2013, 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 barback.asset_provider;
-
-import 'dart:async';
-
-import 'asset.dart';
-import 'asset_id.dart';
-import 'transformer.dart';
-
-// TODO(nweiz): change the name of this class now that it provides more than
-// just assets.
-/// API for locating and accessing packages on disk.
-///
-/// Implemented by pub and provided to barback so that it isn't coupled
-/// directly to pub.
-abstract class AssetProvider {
-  /// The names of all packages that can be provided by this provider.
-  ///
-  /// This is equal to the transitive closure of the entrypoint package
-  /// dependencies.
-  Iterable<String> get packages;
-
-  // TODO(rnystrom): Make this async.
-  /// The paths of all available asset files in [package], relative to the
-  /// package's root directory.
-  ///
-  /// You can pass [within], which should be the relative path to a directory
-  /// within the package, to only return the files within that subdirectory.
-  List<AssetId> listAssets(String package, {String within});
-
-  /// Returns the list of transformer phases that are applicable to [package].
-  ///
-  /// The phases will be run in sequence, with the outputs of one pipelined into
-  /// the next. All [Transformer]s in a single phase will be run in parallel.
-  Iterable<Iterable<Transformer>> getTransformers(String package);
-
-  Future<Asset> getAsset(AssetId id);
-}