Add a "librarySource" field to CompilationUnitElementImpl.

pkg/analyzer/lib/src/task/task_dart.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 engine.task.dart;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
@@ skipping 64 matching lines @@
    * Return the compilation unit element that was produced, or `null` if the
    * task has not yet been performed or if an exception occurred.
    */
   CompilationUnitElement getUnitElement() {
     return unitElement;
   }
 
   @override
   void internalPerform() {
     CompilationUnitBuilder builder = new CompilationUnitBuilder();
-    unitElement = builder.buildCompilationUnit(source, unit);
+    unitElement = builder.buildCompilationUnit(source, unit, library);
   }
 }