Merge pull request #12481 from practicalswift/swiftc-28862-swift-prot…

…ocoldecl-getinheritedprotocols-const

[swiftc (68 vs. 5600)] Add crasher in swift::TypeBase::getCanonicalType(...)

validation-test/compiler_crashers/28862-swift-protocoldecl-getinheritedprotocols-const.swift

@@ -0,0 +1,12 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// RUN: not --crash %target-swift-frontend %s -emit-ir
+protocol A:RangeReplaceableCollection&(t:A{extension{}a e:class a{}class a
+{{}lass a=_{case.a<a =nil??as?=
+:a<a
+?as?=