Pass in "mode" to transformer plugins.

pkg/barback/lib/src/barback_settings.dart

Index: pkg/barback/lib/src/barback_settings.dart
diff --git a/pkg/barback/lib/src/barback_settings.dart b/pkg/barback/lib/src/barback_settings.dart
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+// Copyright (c) 2013, 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.
+
+library barback.barback_settings;
+
+/// A generic settings object for providing configuration details to
+/// [Transformer]s.
+///
+/// Barback does not specify *how* this is provided to transformers. It is up
+/// to a host application to handle this. (For example, pub passes this to the
+/// transformer's constructor.)
+class BarbackSettings {
+  /// An open-ended map of configuration properties specific to this
+  /// transformer.
+  ///
+  /// The contents of the map should be serializable across isolates, but
+  /// otherwise can contain whatever you want.
+  final Map configuration;
+
+  /// The mode that user is running Barback in.
+  ///
+  /// This will be the same for all transformers in a running instance of
+  /// Barback.
+  final BarbackMode mode;
+
+  BarbackSettings(this.configuration, this.mode);
+}
+
+/// Enum-like class for specifying a mode that transformers may be run in.
+///
+/// Note that this is not a *closed* set of enum values. Host applications may
+/// define their own values for this, so a transformer relying on it should
+/// ensure that it behaves sanely with unknown values.
+class BarbackMode {
+  /// The normal mode used during development.
+  static const DEBUG = const BarbackMode._("debug");
+
+  /// The normal mode used to build an application for deploying to production.
+  static const RELEASE = const BarbackMode._("release");
+
+  /// The name of the mode.
+  ///
+  /// By convention, this is a lowercase string.
+  final String name;
+
+  /// Create a mode named [name].
+  factory BarbackMode(String name) {
+    // Use canonical instances of known names.
+    switch (name) {
+      case "debug": return BarbackMode.DEBUG;
+      case "release": return BarbackMode.RELEASE;
+      default:
+        return new BarbackMode._(name);
+    }
+  }
+
+  const BarbackMode._(this.name);
+
+  String toString() => name;
+}