If we made progress, add testCases to the front of the queue in test_runner.dart

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 54800d2fd9122e80096349834fe3db42bbdf60a3..7afb4667e50399511fb9bec806883f89d7161c4a 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -1665,7 +1665,7 @@ class ProcessQueue {
             _progress.done(testCase);
             if (testCase is BrowserTestCase) testCase.notifyObservers();
           } else {
-            _tests.add(testCase);
+            _tests.addFirst(testCase);

[ngeoffray, 2013/01/31 12:56:31]

I thought you could not do this because if it's an IE command, and IE is taken,
you would wait for it.

[kustermann, 2013/01/31 13:01:17]

Well, I was kind of stupid. It's save to put it into the front of the queue if
we actually made some progress (for example if we did run a compilation
command). But if we dequeue it from the front and there is no slot available we
HAVE to put it on the end. (which is on line 1620).

           }
           _tryRunTest();
         });