Decide if unit without directives is a part or a library.

pkg/analyzer/test/src/context/context_test.dart

Index: pkg/analyzer/test/src/context/context_test.dart
diff --git a/pkg/analyzer/test/src/context/context_test.dart b/pkg/analyzer/test/src/context/context_test.dart
index 71040cab47f4055d2e09140448c02ad87222ef76..dbaf418c56e20ff80fe0dd0ff998c093d3214823 100644
--- a/pkg/analyzer/test/src/context/context_test.dart
+++ b/pkg/analyzer/test/src/context/context_test.dart
@@ -554,10 +554,7 @@ part of lib;
         reason: "part resolved 3");
   }
 
-  void fail_performAnalysisTask_changePartContents_makeItAPart() {
-    // TODO(paulberry): fix this.  It appears to be broken because of broken
-    // dependency handling with part files (see TODO comment in
-    // ContainingLibrariesTask.internalPeform)
+  void test_performAnalysisTask_changePartContents_makeItAPart() {
     Source libSource = addSource("/lib.dart", r'''
 library lib;
 part 'part.dart';