Add margin to browser tests and not VM...

tests/lib/async/multiple_timer_test.dart

Index: tests/lib/async/multiple_timer_test.dart
diff --git a/tests/lib/async/multiple_timer_test.dart b/tests/lib/async/multiple_timer_test.dart
index 824ced6b0270c2e469ab80dd59dadcb2ddbc583b..0a57ef012b6b496c46cc3de82f24bde4a84fef7c 100644
--- a/tests/lib/async/multiple_timer_test.dart
+++ b/tests/lib/async/multiple_timer_test.dart
@@ -18,7 +18,7 @@ const Duration TIMEOUT4 = const Duration(milliseconds: 1500);
 // Some browsers (Firefox and IE so far) can trigger too early. So we add more
 // margin. We use identical(1, 1.0) as an easy way to know if the test is
 // compiled by dart2js.
-int get safetyMargin => identical(1, 1.0) ? 1 : 100;
+int get safetyMargin => identical(1, 1.0) ? 100 : 1;
 
 main() {
   test("multiple timer test", () {