Turn on ui impl-side painting by default

chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc

Index: chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc
diff --git a/chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc b/chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc
index de641da25aba536632a26c23e6cf74d699851410..afb3c6edd8a6e2ff9a4f9da518bd7311112ab848 100644
--- a/chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc
+++ b/chrome/browser/chromeos/login/screenshot_testing/screenshot_testing_mixin.cc
@@ -27,7 +27,8 @@ void ScreenshotTestingMixin::SetUpInProcessBrowserTestFixture() {
 void ScreenshotTestingMixin::SetUpCommandLine(base::CommandLine* command_line) {
   if (enable_test_screenshots_) {
     command_line->AppendSwitch(switches::kEnablePixelOutputInTests);
-    command_line->AppendSwitch(switches::kUIEnableImplSidePainting);
+  } else {
+    command_line->AppendSwitch(switches::kUIDisableImplSidePainting);
   }
 }