Add a "librarySource" field to CompilationUnitElementImpl.

pkg/analyzer/lib/src/generated/testing/element_factory.dart

Index: pkg/analyzer/lib/src/generated/testing/element_factory.dart
diff --git a/pkg/analyzer/lib/src/generated/testing/element_factory.dart b/pkg/analyzer/lib/src/generated/testing/element_factory.dart
index 497990c91cd366320bc04c0cd58673c8aa18c400..a8d7fff3a88c58133e60222e7f47791610e5bb5a 100644
--- a/pkg/analyzer/lib/src/generated/testing/element_factory.dart
+++ b/pkg/analyzer/lib/src/generated/testing/element_factory.dart
@@ -82,10 +82,15 @@ class ElementFactory {
           [List<String> parameterNames]) =>
       classTypeAlias(typeName, objectType, parameterNames);
 
-  static CompilationUnitElementImpl compilationUnit(String fileName) {
+  static CompilationUnitElementImpl compilationUnit(String fileName,
+      [Source librarySource]) {
     Source source = new NonExistingSource(fileName, UriKind.FILE_URI);
     CompilationUnitElementImpl unit = new CompilationUnitElementImpl(fileName);
     unit.source = source;
+    if (librarySource == null) {
+      librarySource = source;
+    }
+    unit.librarySource = librarySource;
     return unit;
   }