Fix build failure at src/qtwebkit/viewwindowmgr.cpp

In some cases compilation of the src/qtwebkit/viewwindowmgr.cpp
file failed with the message "error: invalid use of incomplete
type 'class QTabBar'".

This patch adds the missing include statement.

Author: arzam16

src/qtwebkit/viewwindowmgr.cpp

@@ -17,6 +17,7 @@
  */
 
 #include <QClipboard>
+#include <QTabBar>
 #include <QMouseEvent>
 
 #include "../i18n.h"