Add BaseTransform.consumePrimary to barback.

pkg/barback/test/transformer/mock.dart

 // 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.test.transformer.mock;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.dart';
@@ skipping 38 matching lines @@
   /// Once this transformer finishes running, this is reset to a new completer,
   /// so it can be used multiple times.
   var _started = new Completer();
 
   /// `true` if any transforms are currently running.
   ///
   /// This is scheduled. The Future will complete at the point in the schedule
   /// that this is called.
   Future<bool> get isRunning => schedule(() => _runningTransforms > 0);
 
+  /// If this is set to `true`, the transformer will consume its primary input
+  /// during [apply].
+  bool consumePrimary = false;
+
   /// Pauses the schedule until this transformer begins running.
   void waitUntilStarted() {
     schedule(() => _started.future, "wait until $this starts");
   }
 
   /// Causes the transformer to pause after running [apply] but before the
   /// returned Future completes.
   ///
   /// This can be resumed by calling [resumeApply]. This operation is scheduled.
   void pauseApply() {
@@ skipping 100 matching lines @@
           return _isPrimary[asset.id].future;
         }
       }).then((_) => result);
     });
   }
 
   Future apply(Transform transform) {
     _numRuns++;
     if (_runningTransforms == 0) _started.complete();
     _runningTransforms++;
+    if (consumePrimary) transform.consumePrimary();
     return newFuture(() => doApply(transform)).then((_) {
       if (_apply != null) return _apply.future;
     }).whenComplete(() {
       _runningTransforms--;
       if (_runningTransforms == 0) _started = new Completer();
     });
   }
 
   /// The wrapped version of [isPrimary] for subclasses to override.
   Future<bool> doIsPrimary(Asset asset);
 
   /// The wrapped version of [doApply] for subclasses to override.
   Future doApply(Transform transform);
 }