Enable the feature BlockingDownloadsInAdFrameWithoutUserActivation

blink LGTMs:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/tXKnmZD3P9o/x5YFru_YBQAJ

Bug: 929911
Change-Id: I0d5ebe43b8c4bca13393035dd3b356ab602ea5b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625781Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662642}

chrome/browser/page_load_metrics/observers/use_counter_page_load_metrics_observer.cc

@@ -70,8 +70,8 @@ void PossiblyWarnFeatureDeprecation(content::RenderFrameHost* rfh,
     case WebFeature::kDownloadInAdFrameWithoutUserGesture:
       rfh->AddMessageToConsole(
           blink::mojom::ConsoleMessageLevel::kWarning,
-          "[Deprecation] Download in ad frame without user activation is "
-          "deprecated and will be removed in M76, around July 2019. See "
+          "[Intervention] Download in ad frame without user activation is "
+          "not allowed. See "
           "https://www.chromestatus.com/feature/6311883621531648 for more "
           "details.");
       return;

third_party/blink/common/features.cc

@@ -14,7 +14,7 @@ namespace features {
 // frame without user activation.
 const base::Feature kBlockingDownloadsInAdFrameWithoutUserActivation{
     "BlockingDownloadsInAdFrameWithoutUserActivation",
-    base::FEATURE_DISABLED_BY_DEFAULT};
+    base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable defer commits a bit to avoid flash.
 const base::Feature kAvoidFlashBetweenNavigation{