Add support for the "external" keyword to summaries.

pkg/analyzer/lib/src/summary/resynthesize.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 summary_resynthesizer;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/element_handle.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 449 matching lines @@
     executableElement.parameters =
         serializedExecutable.parameters.map(buildParameter).toList();
     if (serializedExecutable.returnType != null) {
       executableElement.returnType = buildType(serializedExecutable.returnType);
     } else {
       executableElement.returnType = VoidTypeImpl.instance;
     }
     executableElement.type = new FunctionTypeImpl(executableElement);
     executableElement.hasImplicitReturnType =
         serializedExecutable.hasImplicitReturnType;
+    executableElement.external = serializedExecutable.isExternal;
   }
 
   /**
    * Resynthesize an [ExportElement],
    */
   ExportElement buildExport(UnlinkedExport serializedExport) {
     ExportElementImpl exportElement = new ExportElementImpl(0);
     String exportedLibraryUri = summaryResynthesizer.sourceFactory
         .resolveUri(librarySource, serializedExport.uri)
         .uri
@@ skipping 436 matching lines @@
       elementMap[cls.name] = cls;
     }
     for (FunctionTypeAliasElement typeAlias in unit.functionTypeAliases) {
       elementMap[typeAlias.name] = typeAlias;
     }
     resummarizedElements[absoluteUri] = elementMap;
     unitHolder = null;
     prelinkedUnit = null;
   }
 }