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

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

Index: sdk/lib/_internal/pub_generated/lib/src/source/cached.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/source/cached.dart b/sdk/lib/_internal/pub_generated/lib/src/source/cached.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e3823ea9b03ce7f8ff41a0d9bbb86865264dfc7a
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/source/cached.dart
@@ -0,0 +1,33 @@
+library pub.source.cached;
+import 'dart:async';
+import 'package:path/path.dart' as path;
+import '../io.dart';
+import '../package.dart';
+import '../pubspec.dart';
+import '../source.dart';
+import '../utils.dart';
+abstract class CachedSource extends Source {
+  String get systemCacheRoot => path.join(systemCache.rootDir, name);
+  Future<Pubspec> doDescribe(PackageId id) {
+    return getDirectory(id).then((packageDir) {
+      if (fileExists(path.join(packageDir, "pubspec.yaml"))) {
+        return new Pubspec.load(
+            packageDir,
+            systemCache.sources,
+            expectedName: id.name);
+      }
+      return describeUncached(id);
+    });
+  }
+  Future<Pubspec> describeUncached(PackageId id);
+  Future get(PackageId id, String symlink) {
+    return downloadToSystemCache(id).then((pkg) {
+      createPackageSymlink(id.name, pkg.dir, symlink);
+    });
+  }
+  Future<bool> isInSystemCache(PackageId id) =>
+      getDirectory(id).then(dirExists);
+  Future<Package> downloadToSystemCache(PackageId id);
+  List<Package> getCachedPackages();
+  Future<Pair<int, int>> repairCachedPackages();
+}