Close variable chooser when pressing escape.

Even if the variable chooser currently doesn't have focus.

Task-number: QTCREATORBUG-7155
Change-Id: Ie3a7527e13dd6c3f37c1abe86a596753d2b8e286
Reviewed-by: Robert Loehning <robert.loehning@digia.com>

src/plugins/coreplugin/variablechooser.h

@@ -58,6 +58,7 @@ public:
 
 protected:
     void keyPressEvent(QKeyEvent *ke);
+    bool eventFilter(QObject *, QEvent *event);
 
 private slots:
     void updateDescription(const QString &variable);