Remove unnecessary casts and general code clean-up

pkg/analyzer/lib/src/context/cache.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.src.context.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/dart/element/element.dart'
@@ skipping 297 matching lines @@
    */
   int _flags = 0;
 
   /**
    * A table mapping result descriptors to the cached values of those results.
    */
   Map<ResultDescriptor, ResultData> _resultMap =
       new HashMap<ResultDescriptor, ResultData>();
 
   CacheEntry(this.target) {
-    if (target is ElementImpl) {
-      (target as ElementImpl).setModifier(Modifier.CACHE_KEY, true);
-    }
+    _markAsCacheKey(target);
   }
 
   /**
    * The exception that caused one or more values to have a state of
    * [CacheState.ERROR].
    */
   CaughtException get exception => _exception;
 
   /**
    * Return `true` if the source was explicitly added to the context or `false`
@@ skipping 294 matching lines @@
     List<TargetedResult> dependentResults = thisData.dependentResults.toList();
     for (TargetedResult dependentResult in dependentResults) {
       CacheEntry entry = _partition.get(dependentResult.target);
       if (entry != null) {
         entry._invalidate(id, dependentResult.result, delta, level);
       }
     }
   }
 
   /**
+   * If the given `target` is an element, mark it as being a cache key.
+   */
+  void _markAsCacheKey(AnalysisTarget target) {
+    if (target is ElementImpl) {
+      target.setModifier(Modifier.CACHE_KEY, true);
+    }
+  }
+
+  /**
    * Set the [dependedOn] on which this result depends.
    */
   void _setDependedOnResults(ResultData thisData, TargetedResult thisResult,
       List<TargetedResult> dependedOn) {
     thisData.dependedOnResults.forEach((TargetedResult dependedOnResult) {
       ResultData data = _partition._getDataFor(dependedOnResult);
       if (data != null) {
         data.dependentResults.remove(thisResult);
       }
     });
@@ skipping 626 matching lines @@
   void resultAccessed(TargetedResult result) {}
 
   @override
   List<TargetedResult> resultStored(TargetedResult newResult, newValue) {
     return TargetedResult.EMPTY_LIST;
   }
 
   @override
   void targetRemoved(AnalysisTarget target) {}
 }