Debugger: Don't add a new watcher item when editing one in-place

Task-number: QTCREATORBUG-14775
Task-number: QTCREATORBUG-14851
Change-Id: I06638ffc2d5a1723e87c1c5a651592e7e0bbad22
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/debugger/watchhandler.h

@@ -153,6 +153,7 @@ public:
 
     void cleanup();
     void watchExpression(const QString &exp, const QString &name = QString());
+    void updateWatchExpression(WatchItem *item, const QByteArray &newExp);
     void watchVariable(const QString &exp);
     Q_SLOT void clearWatches();