Disable BrowserNonClientFrameViewAshTest.AppHeaderVisibilityInTabletModeTest

Disable the test due to flaky.

Bug: 1028336
Tbr: sky@chromium.org
Change-Id: Ibef486c36b878b75a6708b1e567d4f64b1e0cd56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1934317Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718868}

chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc

@@ -1288,7 +1288,7 @@ IN_PROC_BROWSER_TEST_P(BrowserNonClientFrameViewAshTest,
 // Test that for a browser app window, its caption buttons may or may not hide
 // in tablet mode.
 IN_PROC_BROWSER_TEST_P(BrowserNonClientFrameViewAshTest,
-                       AppHeaderVisibilityInTabletModeTest) {
+                       DISABLED_AppHeaderVisibilityInTabletModeTest) {
   // Create a browser app window.
   Browser::CreateParams params = Browser::CreateParams::CreateForApp(
       "test_browser_app", true /* trusted_source */, gfx::Rect(),