Add metrics for app banner preventDefault() and prompt().

chrome/browser/banners/app_banner_data_fetcher.cc

Index: chrome/browser/banners/app_banner_data_fetcher.cc
diff --git a/chrome/browser/banners/app_banner_data_fetcher.cc b/chrome/browser/banners/app_banner_data_fetcher.cc
index 48589c0116663d3e26774bee7ecd8002a1145b9f..a9c2bb19b84b18b628eddb0cbdcf4a4d5f0ef622 100644
--- a/chrome/browser/banners/app_banner_data_fetcher.cc
+++ b/chrome/browser/banners/app_banner_data_fetcher.cc
@@ -188,6 +188,7 @@ void AppBannerDataFetcher::OnBannerPromptReply(
   // Stash the referrer for the case where the banner is redisplayed.
   if (reply == blink::WebAppBannerPromptReply::Cancel &&
       !page_requested_prompt_) {
+    TrackDisplayEvent(DISPLAY_EVENT_CANCELED_BY_PAGE);
     was_canceled_by_page_ = true;
     referrer_ = referrer;
     OutputDeveloperNotShownMessage(web_contents, kRendererRequestCancel,
@@ -212,6 +213,7 @@ void AppBannerDataFetcher::OnRequestShowAppBanner(
   if (was_canceled_by_page_) {
     // Simulate an "OK" from the website to restart the banner display pipeline.
     was_canceled_by_page_ = false;
+    TrackDisplayEvent(DISPLAY_EVENT_PROMPTED_BY_PAGE);
     OnBannerPromptReply(render_frame_host, request_id,
                         blink::WebAppBannerPromptReply::None, referrer_);
   } else {