Re-add missed files

pkg/analyzer/lib/plugin/plugin.dart

Index: pkg/analyzer/lib/plugin/plugin.dart
diff --git a/pkg/analyzer/lib/plugin/plugin.dart b/pkg/analyzer/lib/plugin/plugin.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c81c83c1d2eb81d2e90a99322523423320aee3c6
--- /dev/null
+++ b/pkg/analyzer/lib/plugin/plugin.dart
@@ -0,0 +1,130 @@
+// 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';
+}