Disabled flaky test in ReturnToChromeTest

This CL disables the following test:

* ReturnToChromeTest.testTabSwitcherModeNotTriggeredWithinThreshold_NTP

Because it's flaky on builder:

* Lollipop Tablet Tester

TBR=wychen@chromium.org

Bug: 1144184
Change-Id: Ic5940731985e84fedff4d3bccac0825f4ee7d7f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510356Reviewed-by: Salvador Guerrero <salg@google.com>
Commit-Queue: Salvador Guerrero <salg@google.com>
Cr-Commit-Position: refs/heads/master@{#822704}

chrome/android/javatests/src/org/chromium/chrome/browser/tasks/ReturnToChromeTest.java

@@ -173,6 +173,7 @@ public class ReturnToChromeTest {
     @CommandLineFlags.Add({BASE_PARAMS + "/" + TAB_SWITCHER_ON_RETURN_MS_PARAM + "/100000"
             + "/start_surface_variation/single/open_ntp_instead_of_start/true"})
     @DisableIf.Build(sdk_is_greater_than = VERSION_CODES.O_MR1) // See https://crbug.com/1091268.
+    @DisabledTest(message="https://crbug.com/1144184")
     public void testTabSwitcherModeNotTriggeredWithinThreshold_NTP() throws Exception {
         // clang-format on
         InstantStartTest.createTabStateFile(new int[] {0, 1});