Reenable WidgetTest.WindowModalityActivationTest

This seems to work fine with gtest_repeat=100.

BUG=613428

Change-Id: I045735c4174c8656bfa8d51669142385d35f1233
Reviewed-on: https://chromium-review.googlesource.com/c/1340793Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608989}

ui/views/widget/desktop_aura/desktop_native_widget_aura_unittest.cc

@@ -726,8 +726,7 @@ TEST_F(WidgetTest, WindowMouseModalityTest) {
 #if defined(OS_WIN)
 // Tests whether we can activate the top level widget when a modal dialog is
 // active.
-// Flaky: crbug.com/613428
-TEST_F(WidgetTest, DISABLED_WindowModalityActivationTest) {
+TEST_F(WidgetTest, WindowModalityActivationTest) {
   TestDesktopWidgetDelegate widget_delegate;
   widget_delegate.InitWidget(CreateParams(Widget::InitParams::TYPE_WINDOW));