Fix a type inference corner case: return expression where void expected.

pkg/front_end/testcases/inference/lambda_void_context.dart

Index: pkg/front_end/testcases/inference/lambda_void_context.dart
diff --git a/pkg/front_end/testcases/inference/lambda_void_context.dart b/pkg/front_end/testcases/inference/lambda_void_context.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cf6ddfc34c0bd51a6dbfc055fa9c4e6ecd1a18ba
--- /dev/null
+++ b/pkg/front_end/testcases/inference/lambda_void_context.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2017, 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.
+
+/*@testedFeatures=inference*/
+library test;
+
+f() {
+  List<int> o;
+  o. /*@target=Iterable::forEach*/ forEach(
+      /*@returnType=int*/ (/*@type=int*/ i) => i /*@target=num::+*/ + 1);
+}
+
+main() {}