Try work around issues executing powershell scripts on windows on the bots

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 9f943cd8fd080059c03eacb4ac32aefb9c540508..6bee46513112a772e81e7eb59f94fe60d98fac03 100644
--- a/tools/testing/dart/browser_controller.dart
+++ b/tools/testing/dart/browser_controller.dart
@@ -1907,7 +1907,13 @@ Future captureInternetExplorerScreenshot(String message) async {
   final screenshotFile =
       Platform.script.resolve('../$screenshotName').toFilePath();
 
-  final args = [powerShellScript, screenshotFile];
+  final args = [
+    '-ExecutionPolicy',
+    'ByPass',
+    '-File ',

[ricow1, 2017/04/12 10:25:42]

nit: remove  space after -File?

[kustermann, 2017/04/12 10:27:00]

Done.

+    powerShellScript,
+    screenshotFile
+  ];
   final ProcessResult result =
       await Process.run('powershell.exe', args, runInShell: true);
   if (result.exitCode != 0) {