Fix summary type inference for async closures.

pkg/analyzer/lib/src/summary/link.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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 4654 matching lines @@
 
   void evaluate(bool inCycle) {
     if (inCycle) {
       functionElement._setInferredType(DynamicTypeImpl.instance);
     } else {
       var bodyType = new ExprTypeComputer(functionElement).compute();
       if (functionElement.isAsynchronous) {
         var linker = functionElement.compilationUnit.library._linker;
         var typeProvider = linker.typeProvider;
         var typeSystem = linker.typeSystem;
+        if (bodyType.isDartAsyncFutureOr) {
+          bodyType = (bodyType as InterfaceType).typeArguments[0];
+        }
         bodyType = typeProvider.futureType
             .instantiate([bodyType.flattenFutures(typeSystem)]);
       }
       functionElement._setInferredType(bodyType);
     }
   }
 
   @override
   String toString() => 'TypeInferenceNode($functionElement)';
 }
@@ skipping 310 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }