[filesapp] Don't show JS dialogs in PDF files in Files app QuickView

Bug: 1144419
Change-Id: Ie2872cea95965d15e38dc319897d315f02f9b4b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2635383
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845127}

extensions/browser/guest_view/web_view/javascript_dialog_helper.cc

@@ -51,6 +51,17 @@ void JavaScriptDialogHelper::RunJavaScriptDialog(
     const base::string16& default_prompt_text,
     DialogClosedCallback callback,
     bool* did_suppress_message) {
+  WebViewPermissionHelper* web_view_permission_helper =
+      WebViewPermissionHelper::FromWebContents(web_contents);
+  // crbug.com/1144419: Exit if the permission helper is missing.
+  // TODO(mcnee) - if |web_contents| is an inner MimeHandlerView,
+  // this will be null. We should get the WebViewPermissionHelper
+  // from our WebViewGuest instead.
+  if (!web_view_permission_helper) {
+    std::move(callback).Run(false, base::string16());
+    return;
+  }
+
   base::DictionaryValue request_info;
   request_info.SetString(webview::kDefaultPromptText,
                          base::UTF16ToUTF8(default_prompt_text));
@@ -60,8 +71,7 @@ void JavaScriptDialogHelper::RunJavaScriptDialog(
                          JavaScriptDialogTypeToString(dialog_type));
   request_info.SetString(guest_view::kUrl,
                          render_frame_host->GetLastCommittedURL().spec());
-  WebViewPermissionHelper* web_view_permission_helper =
-      WebViewPermissionHelper::FromWebContents(web_contents);
+
   web_view_permission_helper->RequestPermission(
       WEB_VIEW_PERMISSION_TYPE_JAVASCRIPT_DIALOG, request_info,
       base::BindOnce(&JavaScriptDialogHelper::OnPermissionResponse,