Store the async-await compiled pub code directly in the repo.

sdk/lib/_internal/pub_generated/lib/src/source/unknown.dart

Index: sdk/lib/_internal/pub_generated/lib/src/source/unknown.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/source/unknown.dart b/sdk/lib/_internal/pub_generated/lib/src/source/unknown.dart
new file mode 100644
index 0000000000000000000000000000000000000000..3bcfbacdc725961d8c77eddf1174c707731b8666
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/source/unknown.dart
@@ -0,0 +1,24 @@
+library pub.source.unknown;
+import 'dart:async';
+import '../package.dart';
+import '../pubspec.dart';
+import '../source.dart';
+class UnknownSource extends Source {
+  final String name;
+  UnknownSource(this.name);
+  bool operator ==(other) => other is UnknownSource && other.name == name;
+  int get hashCode => name.hashCode;
+  Future<Pubspec> doDescribe(PackageId id) =>
+      throw new UnsupportedError(
+          "Cannot describe a package from unknown source '$name'.");
+  Future get(PackageId id, String symlink) =>
+      throw new UnsupportedError("Cannot get an unknown source '$name'.");
+  Future<String> getDirectory(PackageId id) =>
+      throw new UnsupportedError(
+          "Cannot find a package from an unknown source '$name'.");
+  bool descriptionsEqual(description1, description2) =>
+      description1 == description2;
+  dynamic parseDescription(String containingPath, description,
+      {bool fromLockFile: false}) =>
+      description;
+}