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

chrome/browser/banners/app_banner_metrics.cc

Index: chrome/browser/banners/app_banner_metrics.cc
diff --git a/chrome/browser/banners/app_banner_metrics.cc b/chrome/browser/banners/app_banner_metrics.cc
index f9bbd34e460afaaf89101bf17b906d6380813973..58e373d3b90f8786c20a60c933a28dcd343ea6f0 100644
--- a/chrome/browser/banners/app_banner_metrics.cc
+++ b/chrome/browser/banners/app_banner_metrics.cc
@@ -15,6 +15,7 @@ const char kInstallEventHistogram[] = "AppBanners.InstallEvent";
 const char kMinutesHistogram[] =
     "AppBanners.MinutesFromFirstVisitToBannerShown";
 const char kUserResponseHistogram[] = "AppBanners.UserResponse";
+const char kBeforeInstallEventHistogram[] = "AppBanners.BeforeInstallEvent";
 
 void TrackDismissEvent(int event) {
   DCHECK_LT(DISMISS_EVENT_MIN, event);
@@ -48,4 +49,10 @@ void TrackUserResponse(int event) {
   UMA_HISTOGRAM_SPARSE_SLOWLY(kUserResponseHistogram, event);
 }
 
+void TrackBeforeInstallEvent(int event) {
+  DCHECK_LT(BEFORE_INSTALL_EVENT_MIN, event);
+  DCHECK_LT(event, BEFORE_INSTALL_EVENT_MAX);
+  UMA_HISTOGRAM_SPARSE_SLOWLY(kBeforeInstallEventHistogram, event);
+}
+
 }  // namespace banners