Add support for specifying files needing analysis

pkg/analysis_server/lib/plugin/analyzed_files.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.
+
+/**
+ * Support for client code that extends the set of files being analyzed by the
+ * analysis server.
+ *
+ * Plugins can register a function that takes a [File] and returns a [bool]
+ * indicating whether the plugin is interested in having that file be analyzed.
+ * The analysis server will invoke the contributed functions and analyze the
+ * file if at least one of the functions returns `true`. (The server is not
+ * required to invoke every function with every file.)
+ */
+library analysis_server.plugin.analyzed_files;
+
+import 'package:analysis_server/edit/assist/assist_core.dart';
+import 'package:analysis_server/src/plugin/server_plugin.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:plugin/plugin.dart';
+
+/**
+ * The identifier of the extension point that allows plugins to register
+ * functions that can cause files to be analyzed. The object used as an
+ * extension must be a [ShouldAnalyzeFile] function.
+ */
+final String ANALYZE_FILE_EXTENSION_POINT_ID = Plugin.join(
+    ServerPlugin.UNIQUE_IDENTIFIER, ServerPlugin.ANALYZE_FILE_EXTENSION_POINT);
+
+/**
+ * A function that returns `true` if the given [file] should be analyzed.
+ */
+typedef bool ShouldAnalyzeFile(File file);