Disable testBackForwardNavigationWithWarningInIncognito

Disable
SafeBrowsingTestCase/testBackForwardNavigationWithWarningInIncognito
on iOS due to flaky.

Bug: 1147360
TBR: ajuma@chromium.org
Change-Id: Iec6462085d66d74af61b838955b3c662e9071aca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2534615Reviewed-by: Owen Min <zmin@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826820}

ios/chrome/browser/safe_browsing/safe_browsing_egtest.mm

@@ -452,7 +452,8 @@ std::unique_ptr<net::test_server::HttpResponse> HandleRequest(
 
 // Tests performing a back navigation to a warning page and a forward navigation
 // from a warning page, in incognito mode.
-- (void)testBackForwardNavigationWithWarningInIncognito {
+// crbug.com/1147360 Test is flaky
+- (void)DISABLED_testBackForwardNavigationWithWarningInIncognito {
   [ChromeEarlGrey openNewIncognitoTab];
   [ChromeEarlGrey loadURL:_safeURL1];
   [ChromeEarlGrey waitForWebStateContainingText:_safeContent1];