MD Settings: Update some dialogs to accept Enter key.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview 'settings-startup-url-dialog' is a component for adding
  * or editing a startup URL entry.
  */
 Polymer({
   is: 'settings-startup-url-dialog',
@@ skipping 49 matching lines @@
         this.browserProxy_.addStartupPage(this.url_);
 
     whenDone.then(function(success) {
       if (success)
         this.$.dialog.close();
       // If the URL was invalid, there is nothing to do, just leave the dialog
       // open and let the user fix the URL or cancel.
     }.bind(this));
   },
 
+  /**
+   * @param {!KeyboardEvent} e
+   * @private
+   */
+  onKeypress_: function(e) {
+    if (e.key == 'Enter' && !this.$.actionButton.disabled)
+      this.onActionButtonTap_();
+  },
+
   /** @private */
   validate_: function() {
     this.browserProxy_.validateStartupPage(this.url_).then(function(isValid) {
       this.$.actionButton.disabled = !isValid;
     }.bind(this));
   },
 });