Add a --mode flag to pub run and pub global run.

sdk/lib/_internal/pub/test/run/mode_test.dart

+// 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 '../descriptor.dart' as d;
+import '../test_pub.dart';
+
+const TRANSFORMER = """
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+class DartTransformer extends Transformer {
+  final BarbackSettings _settings;
+
+  DartTransformer.asPlugin(this._settings);
+
+  String get allowedExtensions => '.in';
+
+  void apply(Transform transform) {
+    transform.addOutput(new Asset.fromString(
+        new AssetId(transform.primaryInput.id.package, "bin/script.dart"),
+        "void main() => print('\${_settings.mode.name}');"));
+  }
+}
+""";
+
+main() {
+  initConfig();
+  withBarbackVersions("any", () {
+    integration('runs a local script with customizable modes', () {
+      d.dir(appPath, [
+        d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/transformer"]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", TRANSFORMER),
+          d.file("primary.in", "")
+        ])])
+      ]).create();
+
+      createLockFile('myapp', pkg: ['barback']);
+
+      // By default it should run in debug mode.
+      var pub = pubRun(args: ["script"]);
+      pub.stdout.expect("debug");
+      pub.shouldExit();
+
+      // A custom mode should be specifiable.
+      pub = pubRun(args: ["--mode", "custom-mode", "script"]);
+      pub.stdout.expect("custom-mode");
+      pub.shouldExit();
+    });
+
+    integration('runs a dependency script with customizable modes', () {
+      d.dir("foo", [
+        d.pubspec({
+          "name": "foo",
+          "version": "1.2.3",
+          "transformers": ["foo/src/transformer"]
+        }),
+        d.dir("lib", [d.dir("src", [
+          d.file("transformer.dart", TRANSFORMER),
+          d.file("primary.in", "")
+        ])])
+      ]).create();
+
+      d.appDir({"foo": {"path": "../foo"}}).create();
+
+      createLockFile('myapp', sandbox: ['foo'], pkg: ['barback']);
+
+      // By default it should run in release mode.
+      var pub = pubRun(args: ["foo:script"]);
+      pub.stdout.expect("release");
+      pub.shouldExit();
+
+      // A custom mode should be specifiable.
+      pub = pubRun(args: ["--mode", "custom-mode", "foo:script"]);
+      pub.stdout.expect("custom-mode");
+      pub.shouldExit();
+    });
+  });
+}