Disable PageAdDensityIgnoreDisplayNoneFrame for real.

CL:2371729 didn't actually disable it.
Still flaky.

TBR=justinmiron@chromium.org,fergal@chromium.org

Bug: 1121444
Change-Id: Ia9f55651c33b8139e2646fc25d084f2fd433b2dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2403360Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805712}

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

@@ -433,7 +433,7 @@ IN_PROC_BROWSER_TEST_F(AdsPageLoadMetricsObserverBrowserTest,
   PageAdDensityIgnoreDisplayNoneFrame
 #endif
 IN_PROC_BROWSER_TEST_F(AdsPageLoadMetricsObserverBrowserTest,
-                       PageAdDensityIgnoreDisplayNoneFrame) {
+                       MAYBE_PageAdDensityIgnoreDisplayNoneFrame) {
   base::HistogramTester histogram_tester;
   ukm::TestAutoSetUkmRecorder ukm_recorder;
   auto waiter = CreatePageLoadMetricsTestWaiter();