Merge pull request #1669 from practicalswift/swiftc-28269-swift-expr-walk

[swiftc] Add test case for crash triggered in swift::Expr::walk(…)

Author: practicalswift

validation-test/compiler_crashers/28269-swift-expr-walk.swift

@@ -0,0 +1,10 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// RUN: not --crash %target-swift-frontend %s -parse
+// REQUIRES: asserts
+protocol A.struct B<f func a<T:A{class A{var t:B=