Add a "librarySource" field to CompilationUnitElementImpl.

pkg/analyzer/test/generated/element_test.dart

Index: pkg/analyzer/test/generated/element_test.dart
diff --git a/pkg/analyzer/test/generated/element_test.dart b/pkg/analyzer/test/generated/element_test.dart
index 4e8041de7a358abac556d23de1d1d8c78e5c51ab..0de22892c8d44172e8bb3b5ba17ca99d5b527401 100644
--- a/pkg/analyzer/test/generated/element_test.dart
+++ b/pkg/analyzer/test/generated/element_test.dart
@@ -3563,9 +3563,9 @@ class LibraryElementImplTest extends EngineTestCase {
     LibraryElementImpl library = ElementFactory.library(context, "test");
     CompilationUnitElement unitLib = library.definingCompilationUnit;
     CompilationUnitElementImpl unitA =
-        ElementFactory.compilationUnit("unit_a.dart");
+        ElementFactory.compilationUnit("unit_a.dart", unitLib.source);
     CompilationUnitElementImpl unitB =
-        ElementFactory.compilationUnit("unit_b.dart");
+        ElementFactory.compilationUnit("unit_b.dart", unitLib.source);
     library.parts = <CompilationUnitElement>[unitA, unitB];
     expect(library.units,
         unorderedEquals(<CompilationUnitElement>[unitLib, unitA, unitB]));