Implement unregisterProtocolHandler() function on CUSTOM_SCHEME_HANDLER

LayoutTests/fast/dom/unregister-protocol-handler.html

Index: LayoutTests/fast/dom/unregister-protocol-handler.html
diff --git a/LayoutTests/fast/dom/unregister-protocol-handler.html b/LayoutTests/fast/dom/unregister-protocol-handler.html
index 609726662a994ec463aa715a7490d7701aa4321a..0a299be14405d3d2a9030ac6a014bae6914fb62b 100644
--- a/LayoutTests/fast/dom/unregister-protocol-handler.html
+++ b/LayoutTests/fast/dom/unregister-protocol-handler.html
@@ -54,11 +54,11 @@ invalid_urls.forEach(function (url) {
    try {
         window.navigator.unregisterProtocolHandler('web+myprotocol', url, 'title');
     } catch (e) {
-        succeeded = 'SYNTAX_ERR' == e.name;
+        succeeded = 'SyntaxError' == e.name;
     }
 
     if (succeeded)
-        debug('Pass: Invalid url "' + url + '" threw SYNTAX_ERR exception.');
+        debug('Pass: Invalid url "' + url + '" threw SyntaxError exception.');
     else
         debug('Fail: Invalid url "' + url + '" allowed.');
 });