[Sheriff] Disable testContextMenu..._NoDefaultSearchEngine

Marks
  org.chromium.chrome.browser.contextmenu.ContextMenuTest
    #testContextMenuRetrievesImageOptions_NoDefaultSearchEngine
as flaky on Android Nexus 5.

TBR=tedchoc@chromium.org

BUG=chromium:988891
TEST=None

Change-Id: Iee2e866aafb57024641a88ac58750aff8a86137d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724524Reviewed-by: Lutz Justen <ljusten@chromium.org>
Commit-Queue: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682192}

chrome/android/javatests/src/org/chromium/chrome/browser/contextmenu/ContextMenuTest.java

@@ -397,6 +397,7 @@ public class ContextMenuTest implements CustomMainActivityStart {
     @SmallTest
     @Feature({"Browser", "ContextMenu"})
     @Policies.Add({ @Policies.Item(key = "DefaultSearchProviderEnabled", string = "false") })
+    @FlakyTest(message = "http://crbug.com/988891")
     @RetryOnFailure
     public void testContextMenuRetrievesImageOptions_NoDefaultSearchEngine()
             throws TimeoutException, InterruptedException {