Replace ResultProvider with 'aboutToComputeResult'.

pkg/analyzer/lib/src/generated/engine.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 analyzer.src.generated.engine;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 1869 matching lines @@
    * Sets the [TypeProvider] for this context.
    */
   void set typeProvider(TypeProvider typeProvider);
 
   /**
    * A list of all [WorkManager]s used by this context.
    */
   List<WorkManager> get workManagers;
 
   /**
+   * This method is invoked when the state of the [result] of the [entry] is
+   * [CacheState.INVALID], so it is about to be computed.
+   *
+   * If the context knows how to provide the value, it sets the value into
+   * the [entry] with all required dependencies, and returns `true`.
+   *
+   * Otherwise, it returns `false` to indicate that the result should be
+   * computed as usually.
+   */
+  bool aboutToComputeResult(CacheEntry entry, ResultDescriptor result);
+
+  /**
    * Return a list containing the sources of the libraries that are exported by
    * the library with the given [source]. The list will be empty if the given
    * source is invalid, if the given source does not represent a library, or if
    * the library does not export any other libraries.
    *
    * Throws an [AnalysisException] if the exported libraries could not be
    * computed.
    */
   List<Source> computeExportedLibraries(Source source);
 
@@ skipping 496 matching lines @@
    * The data that was created from the source.
    */
   final E data;
 
   /**
    * Initialize a newly created holder to associate the given [data] with the
    * given [modificationTime].
    */
   TimestampedData(this.modificationTime, this.data);
 }