Have the editor list combo adjust size to contents

Now the box will grow larger when files with long filenames are opened.

src/plugins/coreplugin/editormanager/stackededitorgroup.cpp

@@ -79,6 +79,7 @@ StackedEditorGroup::StackedEditorGroup(QWidget *parent) :
     tl->setMargin(0);
     {
         m_editorList->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
+        m_editorList->setSizeAdjustPolicy(QComboBox::AdjustToContents);
         m_editorList->setMinimumContentsLength(20);
         m_proxyModel.setSourceModel(model());
         m_proxyModel.sort(0);