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

sdk/lib/_internal/pub_generated/lib/src/barback/cycle_exception.dart

Index: sdk/lib/_internal/pub_generated/lib/src/barback/cycle_exception.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback/cycle_exception.dart b/sdk/lib/_internal/pub_generated/lib/src/barback/cycle_exception.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b516cd7ea0912c33a996c9649080ec3ca2fbe3a8
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/barback/cycle_exception.dart
@@ -0,0 +1,29 @@
+library pub.barback.cycle_exception;
+import '../exceptions.dart';
+class CycleException implements ApplicationException {
+  final String _step;
+  final CycleException _next;
+  List<String> get steps {
+    if (_step == null) return [];
+    var exception = this;
+    var steps = [];
+    while (exception != null) {
+      steps.add(exception._step);
+      exception = exception._next;
+    }
+    return steps;
+  }
+  String get message {
+    var steps = this.steps;
+    if (steps.isEmpty) return "Transformer cycle detected.";
+    return "Transformer cycle detected:\n" +
+        steps.map((step) => "  $step").join("\n");
+  }
+  CycleException([this._step]) : _next = null;
+  CycleException._(this._step, this._next);
+  CycleException prependStep(String step) {
+    if (_step == null) return new CycleException(step);
+    return new CycleException._(step, this);
+  }
+  String toString() => message;
+}