In the new task model, use explicit dependencies on the type provider.

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/src/cancelable_future.dart';
@@ skipping 402 matching lines @@
   }
 
   set test_incrementalAnalysisCache(IncrementalAnalysisCache value) {
     _incrementalAnalysisCache = value;
   }
 
   List<Source> get test_priorityOrder => _priorityOrder;
 
   @override
   TypeProvider get typeProvider {
+    // Make sure a task didn't accidentally try to call back into the context
+    // to retrieve the type provider.
+    assert(!driver.isTaskRunning);
+
     if (_typeProvider != null) {
       return _typeProvider;
     }
     Source coreSource = sourceFactory.forUri(DartSdk.DART_CORE);
     if (coreSource == null) {
       throw new AnalysisException("Could not create a source for dart:core");
     }
     LibraryElement coreElement = computeLibraryElement(coreSource);
     if (coreElement == null) {
       throw new AnalysisException("Could not create an element for dart:core");
@@ skipping 1601 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, target, computeValue);
     if (!pendingFuture.evaluate(entry)) {
       _context._pendingFutureTargets
           .putIfAbsent(target, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }