Add a "librarySource" field to CompilationUnitElementImpl.

pkg/analyzer/lib/src/task/incremental_element_builder.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.task.incremental_element_builder;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 /**
  * Incrementally updates the existing [unitElement] and builds elements for
  * the [newUnit].
  */
 class IncrementalCompilationUnitElementBuilder {
   final Source source;
+  final Source librarySource;
   final CompilationUnit oldUnit;
   final CompilationUnitElementImpl unitElement;
   final CompilationUnit newUnit;
   final ElementHolder holder = new ElementHolder();
 
   IncrementalCompilationUnitElementBuilder(
       CompilationUnit oldUnit, this.newUnit)
       : oldUnit = oldUnit,
         unitElement = oldUnit.element,
-        source = oldUnit.element.source;
+        source = oldUnit.element.source,
+        librarySource = (oldUnit.element as CompilationUnitElementImpl).librarySource;
 
   void build() {
-    new CompilationUnitBuilder().buildCompilationUnit(source, newUnit);
+    new CompilationUnitBuilder().buildCompilationUnit(
+        source, newUnit, librarySource);
     _processDirectives();
     _processUnitMembers();
     newUnit.element = unitElement;
   }
 
   void _addElementsToHolder(CompilationUnitMember node) {
     List<Element> elements = _getElements(node);
     elements.forEach(_addElementToHolder);
   }
 
@@ skipping 239 matching lines @@
     }
     int oldOffset = element.nameOffset;
     int newOffset = map[oldOffset];
     assert(newOffset != null);
     (element as ElementImpl).nameOffset = newOffset;
     if (element is! LibraryElement) {
       super.visitElement(element);
     }
   }
 }