Add histograms for notices about other forms of browsing history

ios/chrome/browser/ui/webui/history/browsing_history_handler.cc

Index: ios/chrome/browser/ui/webui/history/browsing_history_handler.cc
diff --git a/ios/chrome/browser/ui/webui/history/browsing_history_handler.cc b/ios/chrome/browser/ui/webui/history/browsing_history_handler.cc
index 9ce0c9b8c8fc0a6a5debc7f794686015ff07a691..ea34137a673e82416bd575cb9a795800956af08f 100644
--- a/ios/chrome/browser/ui/webui/history/browsing_history_handler.cc
+++ b/ios/chrome/browser/ui/webui/history/browsing_history_handler.cc
@@ -132,6 +132,11 @@ void GetDeviceNameAndType(const ProfileSyncService* sync_service,
   *type = kDeviceTypeLaptop;
 }
 
+void RecordMetricsForNoticeAboutOtherFormsOfBrowsingHistory(bool shown) {
+  UMA_HISTOGRAM_BOOLEAN("History.ShownHeaderAboutOtherFormsOfBrowsingHistory",
+                        shown);
+}
+
 }  // namespace
 
 BrowsingHistoryHandler::HistoryEntry::HistoryEntry(
@@ -377,6 +382,9 @@ void BrowsingHistoryHandler::QueryHistory(
 
     // Set this to false until the results actually arrive.
     results_info_value_.SetBoolean("hasSyncedResults", false);
+  } else {
+    // The notice could not have been shown, because there is no web history.
+    RecordMetricsForNoticeAboutOtherFormsOfBrowsingHistory(false);
   }
 }
 
@@ -748,6 +756,8 @@ void BrowsingHistoryHandler::WebHistoryQueryComplete(
 void BrowsingHistoryHandler::OtherFormsOfBrowsingHistoryQueryComplete(
     bool found_other_forms_of_browsing_history) {
   has_other_forms_of_browsing_history_ = found_other_forms_of_browsing_history;
+  RecordMetricsForNoticeAboutOtherFormsOfBrowsingHistory(
+      has_other_forms_of_browsing_history_);
   web_ui()->CallJavascriptFunction(
       "showNotification", base::FundamentalValue(has_synced_results_),
       base::FundamentalValue(has_other_forms_of_browsing_history_));