Settings: add missing style import in startup-page dialog

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I7efd3b2fa74cc89768964271b5261ea1593faaab
Reviewed-on: https://chromium-review.googlesource.com/1070767Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561940}

chrome/browser/resources/settings/on_startup_page/startup_url_dialog.html

@@ -4,6 +4,7 @@
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="../i18n_setup.html">
+<link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="startup_urls_page_browser_proxy.html">
 
 <dom-module id="settings-startup-url-dialog">