MD Settings: On Startup, extract dialog to its own file.

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

Index: chrome/browser/resources/settings/on_startup_page/startup_urls_page_browser_proxy.js
diff --git a/chrome/browser/resources/settings/on_startup_page/startup_urls_page_browser_proxy.js b/chrome/browser/resources/settings/on_startup_page/startup_urls_page_browser_proxy.js
index 025748f5009b62b1c763efd7c3182e62cd2c4dae..d286a2f59235d7411a9d9a00454f6fed7a2e3a11 100644
--- a/chrome/browser/resources/settings/on_startup_page/startup_urls_page_browser_proxy.js
+++ b/chrome/browser/resources/settings/on_startup_page/startup_urls_page_browser_proxy.js
@@ -13,11 +13,15 @@ cr.define('settings', function() {
 
     /**
      * @param {string} url
-     * @return {!PromiseResolver<boolean>} Whether the URL is valid.
+     * @return {!Promise<boolean>} Whether the URL is valid.
      */
     validateStartupPage: assertNotReached,
 
-    /** @param {string} url */
+    /**
+     * @param {string} url
+     * @return {!Promise<boolean>} Whether the URL was actually added, or
+     *     ignored because it was invalid.
+     */
     addStartupPage: assertNotReached,
 
     /** @param {number} index */
@@ -45,15 +49,12 @@ cr.define('settings', function() {
 
     /** @override */
     validateStartupPage: function(url) {
-      var resolver = new PromiseResolver();
-      resolver.promise = url.trim().length == 0 ? Promise.resolve(false) :
-          cr.sendWithPromise('validateStartupPage', url);
-      return resolver;
+      return cr.sendWithPromise('validateStartupPage', url);
     },
 
     /** @override */
     addStartupPage: function(url) {
-      chrome.send('addStartupPage', [url.trim()]);
+      return cr.sendWithPromise('addStartupPage', url);
     },
 
     /** @override */