Add unary arithmetic (+#, -#) to ThrowBehaviorVisitor

tests/compiler/dart2js/js_throw_behavior_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.
 
 import 'package:expect/expect.dart';
 import 'package:compiler/src/native/native.dart';
 import 'package:compiler/src/js/js.dart' as js;
 
 void test(String source, NativeThrowBehavior expectedThrowBehavior) {
   js.Template template = js.js.parseForeignJS(source);
@@ skipping 10 matching lines @@
 
   test('0', NEVER);
   test('void 0', NEVER);
   test('#', NEVER);
   test('void #', NEVER);
   test('# + 1', NEVER);
   test('!#', NEVER);
   test('!!#', NEVER);
   test('~#', NEVER);
   test('~~#', NEVER);
+  test('-#', NEVER);
+  test('+#', NEVER);
+  test('-(-#)', NEVER);
+  test('+#', NEVER);
 
   test('# * #', NEVER);
   test('# / #', NEVER);
   test('# % #', NEVER);
   test('# + #', NEVER);
   test('# - #', NEVER);
 
   test('# << #', NEVER);
   test('# >> #', NEVER);
   test('# >>> #', NEVER);
@@ skipping 45 matching lines @@
   test('typeof #', NEVER);
   test('typeof console', NEVER);
   test('typeof foo.#', MAY);
   test('typeof #.foo', NULL_NSM);
 
   test('throw 123', MUST);
   test('throw #', MUST);
   test('throw #.x', MUST);        // Could be better: is also an NSM guard.
   test('throw #.x = 123', MUST);
 }