Preliminary safari support.

lib/src/executable.dart

Index: lib/src/executable.dart
diff --git a/lib/src/executable.dart b/lib/src/executable.dart
index aad1fcd6310a86e7be05ea0110b388ae116df0c7..0173315df98a3226f9a847d6f28384c7ef52fd53 100644
--- a/lib/src/executable.dart
+++ b/lib/src/executable.dart
@@ -72,6 +72,9 @@ bool get _usesTransformer {
 }
 
 void main(List<String> args) {
+  var allPlatforms = TestPlatform.all.toList();
+  if (!Platform.isMacOS) allPlatforms.remove(TestPlatform.safari);
+
   _parser.addFlag("help", abbr: "h", negatable: false,
       help: "Shows this usage information.");
   _parser.addOption("package-root", hide: true);
@@ -85,7 +88,7 @@ void main(List<String> args) {
   _parser.addOption("platform",
       abbr: 'p',
       help: 'The platform(s) on which to run the tests.',
-      allowed: TestPlatform.all.map((platform) => platform.identifier).toList(),
+      allowed: allPlatforms.map((platform) => platform.identifier).toList(),
       defaultsTo: 'vm',
       allowMultiple: true);
   _parser.addOption("concurrency",