Re-enable AdsPageLoadMetricsObserverTest.AdPageLoadUKM

Bug: 1043619

Change-Id: I8a9a1c5f1c7a51e83685aebc02a336ffab6a8011
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2116936Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753330}

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

@@ -1232,7 +1232,7 @@ TEST_F(AdsPageLoadMetricsObserverTest, MemoryCacheAdBytesRecorded) {
 
 // UKM metrics for ad page load are recorded correctly.
 // TODO(crbug.com/1043619) test is flaky on bots.
-TEST_F(AdsPageLoadMetricsObserverTest, DISABLED_AdPageLoadUKM) {
+TEST_F(AdsPageLoadMetricsObserverTest, AdPageLoadUKM) {
   ukm::TestAutoSetUkmRecorder ukm_recorder;
   RenderFrameHost* main_frame = NavigateMainFrame(kNonAdUrl);
   RenderFrameHost* ad_frame = CreateAndNavigateSubFrame(kAdUrl, main_frame);