Re-apply change to move to plugin package

pkg/analyzer/lib/plugin/plugin.dart

-// Copyright (c) 2015, 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 analyzer.plugin.plugin;
-
-/**
- * A function used to register the given [extension] to the extension point with
- * the given unique [identifier].
- *
- * An [ExtensionError] will be thrown if the [extension] is not appropriate
- * for the extension point, such as an [extension] that does not implement the
- * required interface.
- */
-typedef void RegisterExtension(String identifier, Object extension);
-
-/**
- * A function used to register an extension point with the given simple
- * [identifier]. If given, the [validator] will be used to validate extensions
- * to the extension point.
- *
- * An [ExtensionError] will be thrown if the extension point cannot be
- * registered, such as when a plugin attempts to define two extension points
- * with the same simple identifier.
- */
-typedef ExtensionPoint RegisterExtensionPoint(String identifier,
-    [ValidateExtension validateExtension]);
-
-/**
- * A function used by a plugin to validate an [extension] to a extension point.
- *
- * An [ExtensionError] should be thrown if the [extension] is not valid for the
- * extension point, such as an [extension] that does not implement the required
- * interface.
- */
-typedef void ValidateExtension(Object extension);
-
-/**
- * An exception indicating that an error occurred while attempting to register
- * either an extension or an extension point.
- *
- * Clients are not expected to subtype this class.
- */
-class ExtensionError implements Exception {
-  /**
-   * The message describing the error that occurred.
-   */
-  final String message;
-
-  /**
-   * Initialize a newly created error to have the given message.
-   */
-  ExtensionError(this.message);
-}
-
-/**
- * A representation of an extension point.
- *
- * Clients are not expected to subtype this class.
- */
-abstract class ExtensionPoint {
-  /**
-   * Return an immutable list containing all of the extensions that were
-   * registered for this extension point.
-   */
-  List<Object> get extensions;
-
-  /**
-   * Return the plugin that defined this extension point.
-   */
-  Plugin get plugin;
-
-  /**
-   * Return the identifier used to uniquely identify this extension point within
-   * the defining plugin.
-   */
-  String get simpleIdentifier;
-
-  /**
-   * Return the identifier used to uniquely identify this extension point. The
-   * unique identifier is the identifier for the plugin, followed by a period
-   * (`.`), followed by the [simpleIdentifier] for the extension point.
-   */
-  String get uniqueIdentifier;
-}
-
-/**
- * A contribution to the analysis server that can extend the behavior of the
- * server while also allowing other plugins to extend it's behavior.
- *
- * Clients are expected to subtype this class when implementing plugins.
- */
-abstract class Plugin {
-  /**
-   * Return the identifier used to uniquely identify this plugin.
-   */
-  String get uniqueIdentifier;
-
-  /**
-   * Use the [register] function to register all of the extension points
-   * contributed by this plugin.
-   *
-   * Clients should not invoke the [register] function after this method has
-   * returned.
-   */
-  void registerExtensionPoints(RegisterExtensionPoint register);
-
-  /**
-   * Use the [register] function to register all of the extensions contributed
-   * by this plugin.
-   *
-   * Clients should not invoke the [register] function after this method has
-   * returned.
-   */
-  void registerExtensions(RegisterExtension register);
-
-  /**
-   * Return a unique identifier created from the unique identifier from the
-   * [plugin] and the [simpleIdentifier].
-   */
-  static String buildUniqueIdentifier(Plugin plugin, String simpleIdentifier) =>
-      join(plugin.uniqueIdentifier, simpleIdentifier);
-
-  /**
-   * Return an identifier created by joining the [pluginIdentifier] and the
-   * [simpleIdentifier].
-   */
-  static String join(String pluginIdentifier, String simpleIdentifier) =>
-      '$pluginIdentifier.$simpleIdentifier';
-}