Fix two build failures - for typeProvider and findElement.

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/dart/ast/ast.dart';
@@ skipping 448 matching lines @@
             target, iterator.value, false, hintsEnabled, lintsEnabled, sources);
       }
     }
     return new List<Source>.from(sources);
   }
 
   List<Source> get test_priorityOrder => _priorityOrder;
 
   @override
   TypeProvider get typeProvider {
+    // The `AnalysisContextTarget.request` results to into the SDK partition,

[Paul Berry, 2016/06/02 12:09:35]

"to" -> "go"

+    // and the TYPE_PROVIDER result is computed and put into the SDK partition
+    // only by the first non-SDK analysis context. So, in order to reuse it
+    // in other analysis context, we need to ask it from the cache.

[Paul Berry, 2016/06/02 12:09:36]

"in other analysis context, we need to ask it" -> "in other analysis contexts,
we need to ask for it"

+    _typeProvider ??= getResult(AnalysisContextTarget.request, TYPE_PROVIDER);
     if (_typeProvider != null) {
       return _typeProvider;
     }
 
     // Make sure a task didn't accidentally try to call back into the context
     // to retrieve the type provider.
     assert(!driver.isTaskRunning);
 
     Source coreSource = sourceFactory.forUri(DartSdk.DART_CORE);
     if (coreSource == null) {
@@ skipping 1735 matching lines @@
     }
     DartSdk sdk = factory.dartSdk;
     if (sdk == null) {
       throw new IllegalArgumentException(
           "The source factory for an SDK analysis context must have a DartUriResolver");
     }
     return new AnalysisCache(
         <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }