sheriff: disable AdsPageLoadMetricsObserverTest.AdPageLoadUKM

Test is flaky, e.g.:

https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/1958

TBR=csharrison@chromium.org

Bug: 1043619
Change-Id: I1a3356592a50c3cb3018bd0a490547188f0c1137
No-try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2011164Reviewed-by: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733426}

chrome/browser/page_load_metrics/observers/ad_metrics/ads_page_load_metrics_observer_unittest.cc

@@ -1132,7 +1132,8 @@ TEST_F(AdsPageLoadMetricsObserverTest, MemoryCacheAdBytesRecorded) {
 }
 
 // UKM metrics for ad page load are recorded correctly.
-TEST_F(AdsPageLoadMetricsObserverTest, AdPageLoadUKM) {
+// TODO(crbug.com/1043619) test is flaky on bots.
+TEST_F(AdsPageLoadMetricsObserverTest, DISABLED_AdPageLoadUKM) {
   ukm::TestAutoSetUkmRecorder ukm_recorder;
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);