Add "--dry-run" to pub upgrade.

sdk/lib/_internal/pub/test/upgrade/dry_run_does_not_apply_changes_test.dart

Index: sdk/lib/_internal/pub/test/upgrade/dry_run_does_not_apply_changes_test.dart
diff --git a/sdk/lib/_internal/pub/test/upgrade/dry_run_does_not_apply_changes_test.dart b/sdk/lib/_internal/pub/test/upgrade/dry_run_does_not_apply_changes_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..da950b58fffa5bc9299ae56c43f19c41968f28ad
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/upgrade/dry_run_does_not_apply_changes_test.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as path;
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../lib/src/io.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+
+main() {
+  initConfig();
+  integration("--dry-run shows report but does not apply changes", () {
+    servePackages([
+      packageMap("foo", "1.0.0"),
+      packageMap("foo", "2.0.0"),
+    ]);
+
+    // Create the first lockfile.
+    d.appDir({
+      "foo": "1.0.0"
+    }).create();
+
+    pubGet();
+
+    // Change the pubspec.
+    d.appDir({
+      "foo": "any"
+    }).create();
+
+    // Also delete the "packages" directory.
+    schedule(() {
+      deleteEntry(path.join(sandboxDir, appPath, "packages"));
+    });
+
+    // Do the dry run.
+    pubUpgrade(args: ["--dry-run"], output: allOf([
+      contains("> foo 2.0.0 (was 1.0.0)"),
+      contains("Would change 1 dependency.")
+    ]));
+
+    d.dir(appPath, [
+      // The lockfile should be unmodified.
+      d.matcherFile("pubspec.lock", contains("1.0.0")),
+      // The "packages" directory should not have been regenerated.
+      d.nothing("packages")
+    ]).validate();
+  });
+}