MD Settings: validate home button url input

chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js

Index: chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
diff --git a/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js b/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
index b139a7f1494d8067d4e5b4245034d6308fa28ff1..65b7698028c9486cd875423cec6ad8f35d39ba92 100644
--- a/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
+++ b/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
@@ -28,6 +28,12 @@ cr.define('settings', function() {
 // <if expr="is_linux and not chromeos">
     useSystemTheme: assertNotReached,
 // </if>
+
+    /**
+     * @param {string} url The url of which to check validity.
+     * @return {!Promise<boolean>}
+     */
+    validateStartupPage: assertNotReached,
   };
 
   /**
@@ -76,6 +82,11 @@ cr.define('settings', function() {
       chrome.send('useSystemTheme');
     },
 // </if>
+
+    /** @override */
+    validateStartupPage: function(url) {
+      return cr.sendWithPromise('validateStartupPage', url);
+    },
   };
 
   return {