Rename BuildDirectory -> SourceDirectory.

sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart

Index: sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart b/sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart
index beb8c118c5615a5da8f8a0868f4772206e17b6ea..6953d7c02b1b444ce5c52bb07a6dc6f82522a3f1 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/web_socket_api.dart
@@ -11,7 +11,7 @@ import 'package:path/path.dart' as path;
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
 
 import '../utils.dart';
-import 'build_environment.dart';
+import 'asset_environment.dart';
 
 /// Implements the [WebSocket] API for communicating with a running pub serve
 /// process, mainly for use by the Editor.
@@ -20,7 +20,7 @@ import 'build_environment.dart';
 /// methods are described in the method-level documentation below.
 class WebSocketApi {
   final WebSocket _socket;
-  final BuildEnvironment _environment;
+  final AssetEnvironment _environment;
   final _server = new json_rpc.Server();
 
   WebSocketApi(this._socket, this._environment) {