Disable flaky tests on Mac10.11 Tests bot

Disable consistently flaky
SearchEnginePreconnectorNoDelaysBrowserTest.PreconnectSearch test.

See build details below for an example of test failure:
https://ci.chromium.org/p/chromium/builders/ci/Mac10.11%20Tests/56178

Tbr: tbansal@chromium.org
Bug: 1141028
Change-Id: I9f8c8c38ef9fba0cbb339f8fb0f41baa76a9dd68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490408Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819468}

chrome/browser/navigation_predictor/search_engine_preconnector_browsertest.cc

@@ -140,8 +140,9 @@ class SearchEnginePreconnectorNoDelaysBrowserTest
   DISALLOW_COPY_AND_ASSIGN(SearchEnginePreconnectorNoDelaysBrowserTest);
 };
 
+// Test routinely flakes on the Mac10.11 Tests bot (https://crbug.com/1141028).
 IN_PROC_BROWSER_TEST_F(SearchEnginePreconnectorNoDelaysBrowserTest,
-                       PreconnectSearch) {
+                       DISABLED_PreconnectSearch) {
   // Put the fake search URL to be preconnected in foreground.
   NavigationPredictorKeyedServiceFactory::GetForProfile(
       Profile::FromBrowserContext(browser()->profile()))