Add self-reference sources into INCLUDED_PARTS.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index e8443f87e0a9e61b75b5d019f4b110562fc7ffd2..a7518632d80e922b0d46b499749251e2845c0e38 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -2726,9 +2726,7 @@ class ParseDartTask extends SourceBasedAnalysisTask {
             } else if (directive is ImportDirective) {
               explicitlyImportedSourceSet.add(referencedSource);
             } else if (directive is PartDirective) {
-              if (referencedSource != source) {
-                includedSourceSet.add(referencedSource);
-              }
+              includedSourceSet.add(referencedSource);
             } else {
               throw new AnalysisException(
                   '$runtimeType failed to handle a ${directive.runtimeType}');