Add a setting to determine whether showing context menu on mouse up.

Source/web/WebSettingsImpl.cpp

Index: Source/web/WebSettingsImpl.cpp
diff --git a/Source/web/WebSettingsImpl.cpp b/Source/web/WebSettingsImpl.cpp
index 70d3b2a0e74287d9843b2106e8d35def43a40c57..813b16eafc6faf905d8aa90fbc77553f58d5ed15 100644
--- a/Source/web/WebSettingsImpl.cpp
+++ b/Source/web/WebSettingsImpl.cpp
@@ -471,6 +471,11 @@ void WebSettingsImpl::setWebGLErrorsToConsoleEnabled(bool enabled)
     m_settings->setWebGLErrorsToConsoleEnabled(enabled);
 }
 
+void WebSettingsImpl::setShowContextMenuOnMouseUp(bool enabled)
+{
+    m_settings->setShowContextMenuOnMouseUp(enabled);
+}
+
 void WebSettingsImpl::setShowFPSCounter(bool show)
 {
     m_showFPSCounter = show;