Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

pkg/scheduled_test/lib/src/descriptor/directory_descriptor.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 descriptor.directory;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:pathos/path.dart' as path;
@@ skipping 90 matching lines @@
 
     var lastEntryString = prefixLines(contents.last.describe(), prefix: '    ')
         .replaceFirst('    ', "'-- ");
     buffer.write(lastEntryString);
     return buffer.toString();
   }
 }
 
 /// A class for formatting errors thrown by [DirectoryDescriptor].
 class _DirectoryValidationError {
-  final Collection<String> errors;
+  final Iterable<String> errors;
 
   /// Flatten nested [_DirectoryValidationError]s in [errors] to create a single
   /// list of errors.
   static _DirectoryValidationError merge(Iterable errors) {
     return new _DirectoryValidationError(errors.expand((error) {
       if (error is _DirectoryValidationError) return error.errors;
       return [error];
     }));
   }
 
   _DirectoryValidationError(Iterable errors)
       : errors = errors.map((e) => e.toString()).toList();
 
   String toString() {
     if (errors.length == 1) return errors.single;
     return errors.map((e) => prefixLines(e, prefix: '  ', firstPrefix: '* '))
         .join('\n');
   }
 }