Mac: restore focus to last active browser after showing app modal dialog

Bug: 1143589
Change-Id: Ic9d59025575fa264c81384dbc11b531d0b7a227c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2640834Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845662}

chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm

@@ -13,6 +13,9 @@
 #include "base/memory/ptr_util.h"
 #import "chrome/browser/chrome_browser_application_mac.h"
 #include "chrome/browser/ui/blocked_content/popunder_preventer.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_list.h"
+#include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/javascript_dialogs/chrome_javascript_app_modal_dialog_view_factory.h"
 #include "components/javascript_dialogs/app_modal_dialog_controller.h"
 #include "components/javascript_dialogs/app_modal_dialog_manager.h"
@@ -106,6 +109,8 @@ void JavaScriptAppModalDialogCocoa::OnAlertFinished(
       controller_->OnClose();
       break;
   }
+  if (Browser* browser = BrowserList::GetInstance()->GetLastActive())
+    browser->window()->Show();
   delete this;
 }