Pass a package root to spawned isolates in pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.dart b/sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.dart
index e2e84e58162bc93e783507f7889dbdedc4c82ed5..8a563e922fa945885a4099a3244ca0b4d8c4bd08 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/transformer_isolate.dart
@@ -58,8 +58,7 @@ class TransformerIsolate {
       var baseUrl = transformerServer.url;
       var idsToUrls = mapMap(idsToAssetIds, value: (id, assetId) {
         var path = assetId.path.replaceFirst('lib/', '');
-        // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
-        return baseUrl.resolve('packages/${id.package}/$path');
+        return Uri.parse('package:${id.package}/$path');
       });
 
       var code = new StringBuffer();
@@ -70,7 +69,7 @@ class TransformerIsolate {
       }
 
       code.writeln("import "
-          "r'$baseUrl/packages/\$pub/transformer_isolate.dart';");
+          "r'package:\$pub/transformer_isolate.dart';");

[Bob Nystrom, 2014/09/23 21:56:11]

Will this fit on one line now?

[nweiz, 2014/09/23 23:23:58]

Done.

       code.writeln(
           "void main(_, SendPort replyTo) => loadTransformers(replyTo);");
 
@@ -78,6 +77,7 @@ class TransformerIsolate {
 
       var port = new ReceivePort();
       return dart.runInIsolate(code.toString(), port.sendPort,
+              packageRoot: baseUrl.resolve('packages'),
               snapshot: snapshot)
           .then((_) => port.first)
           .then((sendPort) {
@@ -113,11 +113,7 @@ class TransformerIsolate {
   /// return an empty set.
   Future<Set<Transformer>> create(TransformerConfig config) {
     return call(_port, {
-      // TODO(nweiz): Right now, we can load a library either from a running
-      // server or from a snapshot. This means the base URL isn't known except
-      // in the isolate, so we pass just the path.component and let the isolate
-      // resolve it. When issue 12474 is fixed, we can send the full URL.
-      'library': _idsToUrls[config.id].path.toString(),
+      'library': _idsToUrls[config.id].toString(),
       'mode': _mode.name,
       'configuration': JSON.encode(config.configuration)
     }).then((transformers) {