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

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

Index: sdk/lib/_internal/pub_generated/lib/src/barback.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback.dart b/sdk/lib/_internal/pub_generated/lib/src/barback.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8e1707aa871ee04979323fdf4fbfcb8b4c4a2d84
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/barback.dart
@@ -0,0 +1,31 @@
+library pub.barback;
+import 'package:barback/barback.dart';
+import 'package:path/path.dart' as p;
+import 'version.dart';
+final pubConstraints = {
+  "barback": new VersionConstraint.parse(">=0.13.0 <0.15.1"),
+  "source_span": new VersionConstraint.parse(">=1.0.0 <2.0.0"),
+  "stack_trace": new VersionConstraint.parse(">=0.9.1 <2.0.0")
+};
+Uri idToPackageUri(AssetId id) {
+  if (!id.path.startsWith('lib/')) {
+    throw new ArgumentError("Asset id $id doesn't identify a library.");
+  }
+  return new Uri(
+      scheme: 'package',
+      path: p.url.join(id.package, id.path.replaceFirst('lib/', '')));
+}
+AssetId packagesUrlToId(Uri url) {
+  var parts = p.url.split(url.path);
+  if (parts.isNotEmpty && parts.first == "/") parts = parts.skip(1).toList();
+  if (parts.isEmpty) return null;
+  var index = parts.indexOf("packages");
+  if (index == -1) return null;
+  if (parts.length <= index + 1) {
+    throw new FormatException(
+        'Invalid URL path "${url.path}". Expected package name ' 'after "packages".');
+  }
+  var package = parts[index + 1];
+  var assetPath = p.url.join("lib", p.url.joinAll(parts.skip(index + 2)));
+  return new AssetId(package, assetPath);
+}