[Sheriff] Disable flaky test testShow_SingleAsHomepage_NoIncognitoSwitch

Bug: 1139515
Change-Id: I0a34783a6a58581fcb64560c11ac5538db369553
TBR: wychen@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500427Reviewed-by: Patrick Noland <pnoland@chromium.org>
Commit-Queue: Patrick Noland <pnoland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820999}

chrome/android/features/start_surface/internal/javatests/src/org/chromium/chrome/features/start_surface/StartSurfaceTest.java

@@ -436,6 +436,7 @@ public class StartSurfaceTest {
     @MediumTest
     @Feature({"StartSurface"})
     @CommandLineFlags.Add({BASE_PARAMS + "/single/hide_incognito_switch/true"})
+    @FlakyTest(message = "https://crbug.com/1139515")
     public void testShow_SingleAsHomepage_NoIncognitoSwitch() {
         if (!mImmediateReturn) {
             onView(withId(org.chromium.chrome.tab_ui.R.id.home_button)).perform(click());