Use precompiled dependencies in pub.

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

Index: sdk/lib/_internal/pub_generated/lib/src/cached_package.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/cached_package.dart b/sdk/lib/_internal/pub_generated/lib/src/cached_package.dart
new file mode 100644
index 0000000000000000000000000000000000000000..dc9fa40038c0d4da56b3a6f1858f933fe80a9396
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/cached_package.dart
@@ -0,0 +1,48 @@
+library pub.cached_package;
+import 'package:path/path.dart' as p;
+import 'package:yaml/yaml.dart';
+import 'barback/transformer_config.dart';
+import 'io.dart';
+import 'package.dart';
+import 'pubspec.dart';
+import 'version.dart';
+class CachedPackage extends Package {
+  final String _cacheDir;
+  CachedPackage(Package inner, this._cacheDir)
+      : super(new _CachedPubspec(inner.pubspec), inner.dir);
+  String path(String part1, [String part2, String part3, String part4,
+      String part5, String part6, String part7]) {
+    if (_pathInCache(part1)) {
+      return p.join(_cacheDir, part1, part2, part3, part4, part5, part6, part7);
+    } else {
+      return super.path(part1, part2, part3, part4, part5, part6, part7);
+    }
+  }
+  String relative(String path) {
+    if (p.isWithin(path, _cacheDir)) return p.relative(path, from: _cacheDir);
+    return super.relative(path);
+  }
+  List<String> listFiles({String beneath, recursive: true}) {
+    if (beneath == null) return super.listFiles(recursive: recursive);
+    if (_pathInCache(beneath)) return listDir(p.join(_cacheDir, beneath));
+    return super.listFiles(beneath: beneath, recursive: recursive);
+  }
+  bool _pathInCache(String relativePath) => p.isWithin('lib', relativePath);
+}
+class _CachedPubspec implements Pubspec {
+  final Pubspec _inner;
+  YamlMap get fields => _inner.fields;
+  String get name => _inner.name;
+  Version get version => _inner.version;
+  List<PackageDep> get dependencies => _inner.dependencies;
+  List<PackageDep> get devDependencies => _inner.devDependencies;
+  List<PackageDep> get dependencyOverrides => _inner.dependencyOverrides;
+  PubspecEnvironment get environment => _inner.environment;
+  String get publishTo => _inner.publishTo;
+  Map<String, String> get executables => _inner.executables;
+  bool get isPrivate => _inner.isPrivate;
+  bool get isEmpty => _inner.isEmpty;
+  List<PubspecException> get allErrors => _inner.allErrors;
+  List<Set<TransformerConfig>> get transformers => const [];
+  _CachedPubspec(this._inner);
+}