Delay Firefox browser startup in test scripts, to flatten load.

tools/testing/dart/browser_controller.dart

Index: tools/testing/dart/browser_controller.dart
diff --git a/tools/testing/dart/browser_controller.dart b/tools/testing/dart/browser_controller.dart
index 27765697ea3b74db45fe86f46381cd51199c2df6..7e0b0dfc4b5319b189e4f897456878f8768c575e 100644
--- a/tools/testing/dart/browser_controller.dart
+++ b/tools/testing/dart/browser_controller.dart
@@ -767,7 +767,10 @@ class Firefox extends Browser {
         ];
         var environment = new Map<String, String>.from(Platform.environment);
         environment["MOZ_CRASHREPORTER_DISABLE"] = "1";
-        return startBrowserProcess(_binary, args, environment: environment);
+        // TODO(26060): Remove delay when dart2js stops hanging under load.
+        return new Future.delayed(new Duration(seconds: 10)).then((_) {

[Siggi Cherem (dart-lang), 2016/04/25 18:21:41]

since this is only causing issues in windows, can we conditionally perform the
delay only there?

[Bill Hesse, 2016/04/26 19:25:08]

We only test on linux and windows, and this delay is not very significant at
all, and this object does not have information about which platform it is
running on.  So I prefer not to do this.  If we need to, we can query the
Platform.isWindows value from dart:io Platform, so it is doable.

+          return startBrowserProcess(_binary, args, environment: environment);
+        });
       });
     }).catchError((e) {
       _logEvent("Running $_binary --version failed with $e");