update completion cache key to include part directives

pkg/analysis_server/lib/src/services/completion/dart_completion_cache.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 services.completion.dart.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element,
@@ skipping 267 matching lines @@
     }
     _importedCompletions.add(suggestion.completion);
   }
 
   /**
    * Compute the hash of the imports for the given compilation unit.
    */
   String _computeImportKey(CompilationUnit unit) {
     StringBuffer sb = new StringBuffer();
     unit.directives.forEach((Directive directive) {
-      if (directive is ImportDirective) {
-        sb.write(directive.toSource());
-      }
+      sb.write(directive.toSource());
     });
     return sb.toString();
   }
 }
 
 /**
  * A visitor for building suggestions based upon the elements defined by
  * a source file contained in the same library but not the same as
  * the source in which the completions are being requested.
  */
@@ skipping 25 matching lines @@
   @override
   void visitFunctionTypeAliasElement(FunctionTypeAliasElement element) {
     cache.addSuggestion(element, CompletionRelevance.DEFAULT);
   }
 
   @override
   void visitTopLevelVariableElement(TopLevelVariableElement element) {
     cache.addSuggestion(element, CompletionRelevance.DEFAULT);
   }
 }