Disable SBNavigationObserverBrowserTest.AppendRecentNavigationsToEmptyReferrerChain

This test appears to be flaky. Disabling to reduce noise on the CQ and
waterfall.

Bug: 1048623
Change-Id: Ib103cf4bc7d2cbc61e355f9ffea2b68052b03291
Tbr: vakh@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2145682Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758317}

chrome/browser/safe_browsing/safe_browsing_navigation_observer_browsertest.cc

@@ -2338,8 +2338,9 @@ IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
           SafeBrowsingNavigationObserverManager::NAVIGATION_EVENT_NOT_FOUND));
 }
 
+// Disabled due to flake: https://crbug.com/1048623
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
-                       AppendRecentNavigationsToEmptyReferrerChain) {
+                       DISABLED_AppendRecentNavigationsToEmptyReferrerChain) {
   ui_test_utils::NavigateToURL(
       browser(), embedded_test_server()->GetURL(kSingleFrameTestURL));
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);