Fix summary generation in "package-summary-only" mode.

pkg/analyzer_cli/lib/src/package_analyzer.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_cli.src.package_analyzer;
 
 import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 76 matching lines @@
         AnalysisResult analysisResult = context.performAnalysisTask();
         if (!analysisResult.hasMoreWork) {
           break;
         }
       }
     }
 
     // Write summary for Dart libraries.
     if (options.packageSummaryOutput != null) {
       PackageBundleAssembler assembler = new PackageBundleAssembler();
-      for (Source source in context.librarySources) {
+      for (Source source in explicitSources) {
+        if (context.computeKindOf(source) != SourceKind.LIBRARY) {
+          continue;
+        }
         if (pathos.isWithin(packageLibPath, source.fullName)) {
           LibraryElement libraryElement = context.computeLibraryElement(source);
-          if (libraryElement != null) {
-            assembler.serializeLibraryElement(libraryElement);
-          }
+          assembler.serializeLibraryElement(libraryElement);
         }
       }
       // Write the whole package bundle.
       PackageBundleBuilder sdkBundle = assembler.assemble();
       io.File file = new io.File(options.packageSummaryOutput);
       file.writeAsBytesSync(sdkBundle.toBuffer(), mode: io.FileMode.WRITE_ONLY);
     }
 
     if (options.packageSummaryOnly) {
       return ErrorSeverity.NONE;
@@ skipping 68 matching lines @@
         sink,
         options,
         (AnalysisError error) =>
             AnalyzerImpl.processError(error, options, context));
     for (Source source in explicitSources) {
       AnalysisErrorInfo errorInfo = context.getErrors(source);
       formatter.formatErrors([errorInfo]);
     }
   }
 }