Use real "package:" imports in pub's plugin-loading code.

sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart

Index: sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart
diff --git a/sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart b/sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart
index ad2c448a4bdd2ad012730f93936ac29d7e271e57..e21c6ffc3bcbce81cac1cd530366b1384e5b957e 100644
--- a/sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart
+++ b/sdk/lib/_internal/pub/asset/dart/transformer_isolate.dart
@@ -2,22 +2,21 @@
 // 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.
 
-// Note: this explicitly avoids using a library tag because pub will add
-// additional imports at the top of the file.
+library pub.transformer_isolate;
 
 import 'dart:async';
 import 'dart:isolate';
 import 'dart:convert';
 import 'dart:mirrors';
 
-import '<<URL_BASE>>/packages/source_maps/span.dart';
-import '<<URL_BASE>>/packages/stack_trace/stack_trace.dart';
-import '<<URL_BASE>>/packages/barback/barback.dart';
+import 'package:source_maps/span.dart';
+import 'package:stack_trace/stack_trace.dart';
+import 'package:barback/barback.dart';
 // TODO(nweiz): don't import from "src" once issue 14966 is fixed.
-import '<<URL_BASE>>/packages/barback/src/internal_asset.dart';
+import 'package:barback/src/internal_asset.dart';
 
 /// Sets up the initial communication with the host isolate.
-void main(_, SendPort replyTo) {
+void loadTransformers(SendPort replyTo) {
   var port = new ReceivePort();
   replyTo.send(port.sendPort);
   port.first.then((wrappedMessage) {
@@ -25,7 +24,7 @@ void main(_, SendPort replyTo) {
       var library = Uri.parse(message['library']);
       var configuration = JSON.decode(message['configuration']);
       var mode = new BarbackMode(message['mode']);
-      return initialize(library, configuration, mode).
+      return _initialize(library, configuration, mode).
           map(_serializeTransformerOrGroup).toList();
     });
   });
@@ -35,7 +34,7 @@ void main(_, SendPort replyTo) {
 ///
 /// Loads the library, finds any Transformer or TransformerGroup subclasses in
 /// it, instantiates them with [configuration] and [mode], and returns them.
-Iterable initialize(Uri uri, Map configuration, BarbackMode mode) {
+Iterable _initialize(Uri uri, Map configuration, BarbackMode mode) {
   var mirrors = currentMirrorSystem();
   var transformerClass = reflectClass(Transformer);
   var groupClass = reflectClass(TransformerGroup);
@@ -109,12 +108,23 @@ class ForeignTransform implements Transform {
   Stream<List<int>> readInput(AssetId id) =>
       _futureStream(getInput(id).then((input) => input.read()));
 
+  Future<bool> hasInput(AssetId id) {
+    return getInput(id).then((_) => true).catchError((error) {
+      if (error is AssetNotFoundException && error.id == id) return false;
+      throw error;
+    });
+  }
+
   void addOutput(Asset output) {
     _call(_port, {
       'type': 'addOutput',
       'output': serializeAsset(output)
     });
   }
+
+  void consumePrimary() {
+    _call(_port, {'type': 'consumePrimary'});
+  }
 }
 
 /// Returns the mirror for the root Object type.