Rename BuildDirectory -> SourceDirectory.

sdk/lib/_internal/pub/lib/src/command/build.dart

Index: sdk/lib/_internal/pub/lib/src/command/build.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/build.dart b/sdk/lib/_internal/pub/lib/src/command/build.dart
index 61e46ef142657d4e0177b530ecb64b38bf03f7e6..560bbe23179d9bdfbed32b6157167ce13e5d5989 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -9,7 +9,7 @@ import 'dart:async';
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as path;
 
-import '../barback/build_environment.dart';
+import '../barback/asset_environment.dart';
 import '../exit_codes.dart' as exit_codes;
 import '../io.dart';
 import '../log.dart' as log;
@@ -53,7 +53,7 @@ class BuildCommand extends BarbackCommand {
     // Since this server will only be hit by the transformer loader and isn't
     // user-facing, just use an IPv4 address to avoid a weird bug on the
     // OS X buildbots.
-    return BuildEnvironment.create(entrypoint, "127.0.0.1", 0, mode,
+    return AssetEnvironment.create(entrypoint, "127.0.0.1", 0, mode,
         WatcherType.NONE, useDart2JS: true)
           .then((environment) {
       // Show in-progress errors, but not results. Those get handled