Add DartSdk.getLinkedBundle() and use it in PubSummaryManager.

pkg/analyzer/lib/src/summary/pub_summary.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 206 matching lines @@
     }
   }
 
   /**
    * Return the list of linked [LinkedPubPackage]s that can be provided at this
    * time for a subset of the packages used by the given [context].  If
    * information about some of the used packages is not available yet, schedule
    * its computation, so that it might be available later for other contexts
    * referencing the same packages.
    */
-  List<LinkedPubPackage> getLinkedBundles(
-      AnalysisContext context, PackageBundle sdkBundle) {
+  List<LinkedPubPackage> getLinkedBundles(AnalysisContext context) {
+    PackageBundle sdkBundle = context.sourceFactory.dartSdk.getLinkedBundle();
+    if (sdkBundle == null) {
+      return const <LinkedPubPackage>[];
+    }
+
     Map<PubPackage, PackageBundle> unlinkedBundles =
         getUnlinkedBundles(context);
 
     // If no unlinked bundles, there is nothing we can try to link.
     if (unlinkedBundles.isEmpty) {
-      return <LinkedPubPackage>[];
+      return const <LinkedPubPackage>[];
     }
 
     // Create graph nodes for packages.
     List<_LinkedNode> nodes = <_LinkedNode>[];
     Map<String, _LinkedNode> packageToNode = <String, _LinkedNode>{};
     unlinkedBundles.forEach((package, unlinked) {
       _LinkedNode node = new _LinkedNode(package, unlinked, packageToNode);
       nodes.add(node);
       packageToNode[package.name] = node;
     });
@@ skipping 372 matching lines @@
           }
         });
         node.linkedBuilder = assembler.assemble();
         store.addBundle(null, node.linkedBuilder);
       }
     } else {
       scc.forEach((node) => node.failed = true);
     }
   }
 }