Clear ClientDownloadResponses when closing chrome://safe-browsing tabs

Change-Id: Iade20c998ceed292eb16595ef23ae30d3bf03202
Reviewed-on: https://chromium-review.googlesource.com/1256013Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595663}

components/safe_browsing/web_ui/safe_browsing_ui.cc

@@ -178,6 +178,7 @@ void WebUIInfoSingleton::UnregisterWebUIInstance(SafeBrowsingUIHandler* webui) {
   if (webui_instances_.empty()) {
     ClearCSBRRsSent();
     ClearClientDownloadRequestsSent();
+    ClearClientDownloadResponsesReceived();
     ClearPGEvents();
     ClearPGPings();
     ClearLogMessages();