Debugger: Simplify thread switching more

This moves the thread switcher combobox, the only consumer
of part of the threadhandler interface, into the threadhandler.

Change-Id: Icafd72e7777fad9196ce8fb33a79cae26c29a521
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/threadshandler.h

@@ -29,6 +29,7 @@
 
 #include <utils/treemodel.h>
 
+#include <QComboBox>
 #include <QPointer>
 
 ////////////////////////////////////////////////////////////////////////
@@ -77,7 +78,6 @@ class ThreadsHandler : public ThreadsHandlerModel
 public:
     explicit ThreadsHandler(DebuggerEngine *engine);
 
-    int currentThreadIndex() const;
     Thread currentThread() const;
     Thread threadForId(const QString &id) const;
     void setCurrentThread(const Thread &thread);
@@ -95,6 +95,8 @@ public:
     void notifyRunning(const QString &id);
     void notifyStopped(const QString &id);
 
+    QComboBox *threadSwitcher() { return m_comboBox; }
+
 private:
     void sort(int column, Qt::SortOrder order) override;
     QVariant data(const QModelIndex &index, int role) const override;
@@ -103,6 +105,7 @@ private:
     DebuggerEngine *m_engine;
     Thread m_currentThread;
     QHash<QString, QString> m_pidForGroupId;
+    QComboBox *m_comboBox;
 };
 
 } // namespace Internal