Handle assert with message in type inference

tests/compiler/dart2js/assert_message_throw_test.dart

+// Copyright (c) 2016, 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.
+
+import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/commandline_options.dart';
+import 'memory_compiler.dart';
+
+const String SOURCE = '''
+main() {
+  assert(true, throw "unreachable");
+  var list = [];

[sra1, 2016/11/26 22:41:20]

I don't understand what this is testing.

Perhaps do something like

var a;
assert(true, (a="Hi"));
var b = a;

b should be inferred as String

[Johnni Winther, 2016/11/28 10:08:29]

The crash reported in #27882. We had inconsistent reasoning on reachable because
we assumed that `throw "unreachable"` always happened. Later code would still
try to access the type info for `list` and crash.

Added more tests.

+}
+''';
+
+main() {
+  asyncTest(() async {
+    await runCompiler(
+        entryPoint: Uri.parse('memory:main.dart'),
+        memorySourceFiles: {'main.dart': SOURCE},
+        options: [Flags.enableCheckedMode, Flags.enableAssertMessage]);
+  });
+}