Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/lib/src/source_registry.dart

Index: sdk/lib/_internal/pub_generated/lib/src/source_registry.dart
diff --git a/sdk/lib/_internal/pub/lib/src/source_registry.dart b/sdk/lib/_internal/pub_generated/lib/src/source_registry.dart
similarity index 94%
copy from sdk/lib/_internal/pub/lib/src/source_registry.dart
copy to sdk/lib/_internal/pub_generated/lib/src/source_registry.dart
index d46ae93ae77299674c4b8004105cf8bf41bb7bf5..fc5b4f38d1f1b9d0869f8118138b0174f00eac7e 100644
--- a/sdk/lib/_internal/pub/lib/src/source_registry.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/source_registry.dart
@@ -58,8 +58,8 @@ class SourceRegistry extends IterableBase<Source> {
   /// registered.
   void register(Source source) {
     if (_sources.containsKey(source.name)) {
-      throw new StateError('Source registry already has a source named '
-          '${source.name}');
+      throw new StateError(
+          'Source registry already has a source named ' '${source.name}');
     }
 
     _sources[source.name] = source;
@@ -69,7 +69,7 @@ class SourceRegistry extends IterableBase<Source> {
   ///
   /// Returns an [UnknownSource] if no source with that name has been
   /// registered. If [name] is null, returns the default source.
-  Source operator[](String name) {
+  Source operator [](String name) {
     if (name == null) {
       if (defaultSource != null) return defaultSource;
       throw new StateError('No default source has been registered');