Fix analyzer type checking of "await" expressions.

pkg/analyzer/test/generated/non_error_resolver_test.dart

 // Copyright (c) 2014, 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 engine.non_error_resolver_test;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
@@ skipping 469 matching lines @@
   void test_async_future_without_return() {
     Source source = addSource('''
 import 'dart:async';
 Future f() async {}
 ''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
+  void test_async_return_flattens_futures() {
+    Source source = addSource('''
+import 'dart:async';
+Future<int> f() async {
+  return g();
+}
+Future<Future<int>> g() => null;
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_async_with_return() {
     Source source = addSource('''
 f() async {
   return;
 }
 ''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
@@ skipping 33 matching lines @@
     Source source = addSource(r'''
 f(list) async* {
   await for (var e in list) {
   }
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
+  void test_await_flattened() {
+    Source source = addSource('''
+import 'dart:async';
+Future<Future<int>> ffi() => null;
+f() async {
+  int b = await ffi();
+}
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
+  void test_await_simple() {
+    Source source = addSource('''
+import 'dart:async';
+Future<int> fi() => null;
+f() async {
+  int a = await fi();
+}
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_awaitInWrongContext_async() {
     Source source = addSource(r'''
 f(x, y) async {
   return await x + await y;
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
@@ skipping 4748 matching lines @@
     resolve(source);
     assertNoErrors(source);
     verify([source]);
     reset();
   }
 
   void _check_wrongNumberOfParametersForOperator1(String name) {
     _check_wrongNumberOfParametersForOperator(name, "a");
   }
 }