Minor clean-up and bug fix

pkg/analysis_server/lib/src/plugin/plugin_locator.dart

 // Copyright (c) 2017, 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:analyzer/file_system/file_system.dart';
 import 'package:yaml/yaml.dart';
 
 /**
  * An object used to locate a plugin within a package.
  */
@@ skipping 33 matching lines @@
    * [resourceProvider] to access the file system.
    */
   PluginLocator(this.resourceProvider);
 
   /**
    * Given the root directory of a package (the [packageRoot]), return the path
    * to the plugin associated with the package, or `null` if there is no plugin
    * associated with the package.
    *
    * This will look first in the `pubspec.yaml` file in the package root for a
-   * key indicating where the plugin is located. If such a key is not defined,
-   * then it will fall back to a well known location within the package.
+   * top-level key (`analysis_plugin`) indicating where the plugin is located.
+   * The value associated with the key is expected to be the path of the plugin
+   * relative to the package root. If the directory exists, the it is returned.
+   *
+   * If the key is not defined in the `pubspec.yaml` file, or if the directory
+   * given does not exist, then this method will look for the directory
+   * `tools/analysis_plugin` relative to the package root. If the directory
+   * exists, the it is returned.

[scheglov, 2017/04/24 15:33:55]

/the/then/s

[Brian Wilkerson, 2017/04/24 15:48:51]

Done

    *
    * This method does not validate the content of the plugin directory before
    * returning it.
    */
   String findPlugin(String packageRoot) {
     return pluginMap.putIfAbsent(packageRoot, () => _findPlugin(packageRoot));
   }
 
   /**
    * The implementation of [findPlugin].
@@ skipping 22 matching lines @@
     }
     Folder pluginFolder = packageFolder
         .getChildAssumingFolder(toolsFolderName)
         .getChildAssumingFolder(defaultPluginFolderName);
     if (pluginFolder.exists) {
       return pluginFolder.path;
     }
     return null;
   }
 }