Support for running a limited amount of browser tests in parallel

tools/test.dart

Index: tools/test.dart
diff --git a/tools/test.dart b/tools/test.dart
index 3077ac6a2f38ea79c979b81006088f1a48756fc0..996893837cd3261ef48da11f3206bfa6bf53c6eb 100755
--- a/tools/test.dart
+++ b/tools/test.dart
@@ -126,7 +126,12 @@ main() {
   }
 
   var testSuites = new List<TestSuite>();
+  var maxBrowserProcesses = maxProcesses;
   for (var conf in configurations) {
+    // We can't run multiple IE processes in parallel.
+    if (conf['runtime'].startsWith('ie')) {
+      maxBrowserProcesses = 1;
+    }
     TestingServerRunner.setPackageRootDir(conf);
     for (String key in selectors.keys) {
       if (key == 'co19') {
@@ -158,6 +163,7 @@ main() {
 
   // Start process queue.
   new ProcessQueue(maxProcesses,
+                   maxBrowserProcesses,
                    progressIndicator,
                    startTime,
                    printTiming,