Reset AnalysisDriver on priority sources changes.

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 285 matching lines @@
       }
       if (sources.isEmpty) {
         _priorityOrder = Source.EMPTY_LIST;
       } else {
         _priorityOrder = sources;
       }
     }
     for (WorkManager workManager in workManagers) {
       workManager.applyPriorityTargets(_priorityOrder);
     }
+    driver.reset();
   }
 
   @override
   set contentCache(ContentCache value) {
     _contentCache = value;
   }
 
   @override
   DeclaredVariables get declaredVariables => _declaredVariables;
 
@@ skipping 1793 matching lines @@
         new PendingFuture<T>(_context, target, computeValue);
     if (!pendingFuture.evaluate(entry)) {
       _context._pendingFutureTargets
           .putIfAbsent(target, () => <PendingFuture>[])
           .add(pendingFuture);
       scheduleComputation();
     }
     return pendingFuture.future;
   }
 }