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

pkg/analyzer/lib/src/context/context.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.context.context;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/instrumentation/instrumentation.dart';
@@ skipping 803 matching lines @@
       return SourceKind.HTML;
     }
     return SourceKind.UNKNOWN;
   }
 
   @override
   List<Source> getLibrariesContaining(Source source) {
     SourceKind kind = getKindOf(source);
     if (kind == SourceKind.LIBRARY) {
       return <Source>[source];
-    } else if (kind == SourceKind.PART) {
-      return dartWorkManager.getLibrariesContainingPart(source);
     }
-    return Source.EMPTY_ARRAY;
+    return dartWorkManager.getLibrariesContainingPart(source);
   }
 
   @override
   List<Source> getLibrariesDependingOn(Source librarySource) {
     List<Source> dependentLibraries = <Source>[];
     for (Source source in _cache.sources) {
       CacheEntry entry = _cache.get(source);
       if (entry.getValue(SOURCE_KIND) == SourceKind.LIBRARY) {
         if (_contains(entry.getValue(EXPORTED_LIBRARIES), librarySource)) {
           dependentLibraries.add(source);
@@ skipping 1184 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, target, computeValue);
     if (!pendingFuture.evaluate(entry)) {
       _context._pendingFutureTargets
           .putIfAbsent(target, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }