Add safetymargin for timer tests in browsers.

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 836e5fcb782519281901e09e61f4115e3bf4b8f8..824ced6b0270c2e469ab80dd59dadcb2ddbc583b 100644
--- a/tests/lib/async/multiple_timer_test.dart
+++ b/tests/lib/async/multiple_timer_test.dart
@@ -12,6 +12,14 @@ const Duration TIMEOUT2 = const Duration(seconds: 2);
 const Duration TIMEOUT3 = const Duration(milliseconds: 500);
 const Duration TIMEOUT4 = const Duration(milliseconds: 1500);
 
+// The stopwatch is more precise than the Timer. It can happen that
+// the TIMEOUT triggers *slightly* too early on the VM. So we add a millisecond
+// as safetymargin.
+// 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;
+
 main() {
   test("multiple timer test", () {
     Stopwatch _stopwatch1 = new Stopwatch();
@@ -22,36 +30,28 @@ main() {
     int _message;
 
     void timeoutHandler1() {
-      // The stopwatch is more precise than the Timer. It can happen that
-      // the TIMEOUT triggers *slightly* too early.
-      expect(_stopwatch1.elapsedMilliseconds + 1,
+      expect(_stopwatch1.elapsedMilliseconds + safetyMargin,
              greaterThanOrEqualTo(TIMEOUT1.inMilliseconds));
       expect(_order[_message], 0);
       _message++;
     }
 
     void timeoutHandler2() {
-      // The stopwatch is more precise than the Timer. It can happen that
-      // the TIMEOUT triggers *slightly* too early.
-      expect(_stopwatch2.elapsedMilliseconds + 1,
+      expect(_stopwatch2.elapsedMilliseconds + safetyMargin,
              greaterThanOrEqualTo(TIMEOUT2.inMilliseconds));
       expect(_order[_message], 1);
       _message++;
     }
 
     void timeoutHandler3() {
-      // The stopwatch is more precise than the Timer. It can happen that
-      // the TIMEOUT triggers *slightly* too early.
-      expect(_stopwatch3.elapsedMilliseconds + 1,
+      expect(_stopwatch3.elapsedMilliseconds + safetyMargin,
              greaterThanOrEqualTo(TIMEOUT3.inMilliseconds));
       expect(_order[_message], 2);
       _message++;
     }
 
     void timeoutHandler4() {
-      // The stopwatch is more precise than the Timer. It can happen that
-      // the TIMEOUT triggers *slightly* too early.
-      expect(_stopwatch4.elapsedMilliseconds + 1,
+      expect(_stopwatch4.elapsedMilliseconds + safetyMargin,
              greaterThanOrEqualTo(TIMEOUT4.inMilliseconds));
       expect(_order[_message], 3);
       _message++;