Disable 2 opt guide incognito browser tests that are flaky

Bug: 1158237,1158257,1158343
Change-Id: I53e17d37f761d64f74e0bb05dc0dba916311876d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2588299
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Auto-Submit: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836671}

chrome/browser/optimization_guide/optimization_guide_keyed_service_browsertest.cc

@@ -618,9 +618,10 @@ IN_PROC_BROWSER_TEST_F(
 #endif
 }
 
+// TODO(crbug/1158343): Re-enable when not flaky.
 IN_PROC_BROWSER_TEST_F(
     OptimizationGuideKeyedServiceDataSaverUserWithInfobarShownTest,
-    IncognitoCanStillReadFromComponentHints) {
+    DISABLED_IncognitoCanStillReadFromComponentHints) {
   // Instantiate off the record Optimization Guide Service.
   OptimizationGuideKeyedServiceFactory::GetForProfile(
       browser()->profile()->GetPrimaryOTRProfile())

chrome/browser/optimization_guide/prediction/prediction_manager_browsertest.cc

@@ -701,9 +701,9 @@ IN_PROC_BROWSER_TEST_F(PredictionManagerBrowserTest,
       1);
 }
 
-IN_PROC_BROWSER_TEST_F(
-    PredictionManagerBrowserTest,
-    DISABLE_ON_WIN_MAC_CHROMEOS(IncognitoDoesntFetchModels)) {
+// TODO(crbug/1158257): Re-enable when not flaky.
+IN_PROC_BROWSER_TEST_F(PredictionManagerBrowserTest,
+                       DISABLED_IncognitoDoesntFetchModels) {
   SetResponseType(PredictionModelsFetcherRemoteResponseType::
                       kSuccessfulWithModelsAndFeatures);
   base::HistogramTester histogram_tester;