Fix analyzer type checking of "await" expressions.

pkg/analyzer/test/generated/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.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 9833 matching lines @@
     // i = 0
     InterfaceType intType = _typeProvider.intType;
     Expression node = AstFactory.assignmentExpression(
         _resolvedVariable(intType, "i"),
         TokenType.EQ,
         _resolvedInteger(0));
     expect(_analyze(node), same(intType));
     _listener.assertNoErrors();
   }
 
+  void test_visitAwaitExpression_flattened() {
+    // await e, where e has type Future<Future<int>>
+    InterfaceType intType = _typeProvider.intType;
+    InterfaceType futureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[intType]);
+    InterfaceType futureFutureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[futureIntType]);
+    Expression node =
+        AstFactory.awaitExpression(_resolvedVariable(futureFutureIntType, 'e'));
+    expect(_analyze(node), same(intType));
+    _listener.assertNoErrors();
+  }
+
+  void test_visitAwaitExpression_simple() {
+    // await e, where e has type Future<int>
+    InterfaceType intType = _typeProvider.intType;
+    InterfaceType futureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[intType]);
+    Expression node =
+        AstFactory.awaitExpression(_resolvedVariable(futureIntType, 'e'));
+    expect(_analyze(node), same(intType));
+    _listener.assertNoErrors();
+  }
+
   void test_visitBinaryExpression_equals() {
     // 2 == 3
     Expression node = AstFactory.binaryExpression(
         _resolvedInteger(2),
         TokenType.EQ_EQ,
         _resolvedInteger(3));
     expect(_analyze(node), same(_typeProvider.boolType));
     _listener.assertNoErrors();
   }
 
@@ skipping 3840 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }