Disable flaky ConstrainedWindowViewsTest.NullModalParent on Windows.

Example:
https://ci.chromium.org/p/chromium/builders/ci/Win10%20Tests%20x64/40963

TBR=wittman@chromium.org

Bug: 1009182
Change-Id: Iafb2ba66e6bc5aa57ee5849d2447933401917f96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829352Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701110}

components/constrained_window/constrained_window_views_unittest.cc

@@ -211,6 +211,12 @@ TEST_F(ConstrainedWindowViewsTest, MaximumWebContentsDialogSize) {
 }
 
 // Ensure CreateBrowserModalDialogViews() works correctly with a null parent.
+// Flaky on Win10. https://crbug.com/1009182
+#if defined(OS_WIN)
+#define MAYBE_NullModalParent DISABLED_NullModalParent
+#else
+#define MAYBE_NullModalParent NullModalParent
+#endif
 TEST_F(ConstrainedWindowViewsTest, NullModalParent) {
   // Use desktop widgets (except on ChromeOS) for extra coverage.
   test_views_delegate()->set_use_desktop_native_widgets(true);