Fix floating dock widget support in debug mode.

The dock widget visibility was not saved/restored correctly, and pulling
floating dock widgets back into the layout didn't remove the header
widget in case of locked mode.
Now we track visibility and floating state of dock widgets directly.

src/plugins/debugger/debuggermanager.h

@@ -217,9 +217,8 @@ public slots:
 
     void setSimpleDockWidgetArrangement();
     void setLocked(bool locked);
-    void setFloatingDockWidgetsVisible(bool visible);
-    void updateDockWidgetActiveStates();
     void dockActionTriggered();
+    void modeVisibilityChanged(bool visible);
 
     void setBusyCursor(bool on);
     void queryCurrentTextEditor(QString *fileName, int *lineNumber, QObject **ed);
@@ -378,6 +377,9 @@ private:
     void runTest(const QString &fileName);
     QDockWidget *createDockForWidget(QWidget *widget);
     Q_SLOT void createNewDock(QWidget *widget);
+    void updateDockWidget(QDockWidget *dockWidget);
+    Q_SLOT void onDockVisibilityChange(bool visible);
+    Q_SLOT void onTopLevelChanged();
 
     void shutdown();
 
@@ -402,6 +404,8 @@ private:
     QDockWidget *m_watchDock;
     QList<QDockWidget*> m_dockWidgets;
     QList<bool> m_dockWidgetActiveState;
+    bool m_locked;
+    bool m_handleDockVisibilityChanges;
 
     BreakHandler *m_breakHandler;
     DisassemblerHandler *m_disassemblerHandler;