Add a setting to disable threaded scrolling

Source/web/WebSettingsImpl.cpp

Index: Source/web/WebSettingsImpl.cpp
diff --git a/Source/web/WebSettingsImpl.cpp b/Source/web/WebSettingsImpl.cpp
index 2aa04457026573513b33ad6fc98ad1b02933e87f..7e2188f734376b4a23cb499aea0d051ccf987b55 100644
--- a/Source/web/WebSettingsImpl.cpp
+++ b/Source/web/WebSettingsImpl.cpp
@@ -401,6 +401,11 @@ void WebSettingsImpl::setAllowFileAccessFromFileURLs(bool allow)
     m_settings->setAllowFileAccessFromFileURLs(allow);
 }
 
+void WebSettingsImpl::setThreadedScrollingEnabled(bool enabled)
+{
+    m_settings->setThreadedScrollingEnabled(enabled);
+}
+
 void WebSettingsImpl::setTouchDragDropEnabled(bool enabled)
 {
     m_settings->setTouchDragDropEnabled(enabled);