Documentation to follow up on CLs 714843002 and 719443002.

dart/pkg/dart2js_incremental/lib/library_updater.dart

 // Copyright (c) 2014, 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 dart2js_incremental.library_updater;
 
 import 'dart:async' show
     Future;
 
 import 'dart:convert' show
@@ skipping 331 matching lines @@
   bool unableToReuse(
       Token diffToken,
       PartialElement before,
       PartialElement after) {
     return cannotReuse(
         after,
         'Unhandled change:'
         ' ${before} (${before.runtimeType} -> ${after.runtimeType}).');
   }
 
+  /// Apply the collected [updates]. Return a list of elements that needs to be
+  /// recompiled after applying the updates. Any elements removed as a
+  /// consequence of applying the patches are added to [removals] if provided.
   List<Element> applyUpdates([List<Update> removals]) {
     for (Update update in updates) {
       update.captureState();
     }
     if (!_failedUpdates.isEmpty) {
       throw new StateError(
           "Can't compute update.\n\n${_failedUpdates.join('\n\n')}");
     }
     for (ElementX element in _elementsToInvalidate) {
       compiler.forgetElement(element);
@@ skipping 382 matching lines @@
 
 abstract class JsFeatures {
   Compiler get compiler;
 
   JavaScriptBackend get backend => compiler.backend;
 
   Namer get namer => backend.namer;
 
   CodeEmitterTask get emitter => backend.emitter;
 }