Project tree: Make code for diff against current file reusable

The same functionality should be available in the file system view.

Change-Id: Ib31cb84924e767ebe06f595bf638a5e674d4f8b5
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/texteditor/textdocument.h

@@ -35,6 +35,7 @@
 #include <QSharedPointer>
 
 QT_BEGIN_NAMESPACE
+class QAction;
 class QTextCursor;
 class QTextDocument;
 QT_END_NAMESPACE
@@ -138,6 +139,9 @@ public:
     void setTabSettings(const TextEditor::TabSettings &tabSettings);
     void setFontSettings(const TextEditor::FontSettings &fontSettings);
 
+    static QAction *createDiffAgainstCurrentFileAction(QObject *parent,
+        const std::function<Utils::FileName()> &filePath);
+
 signals:
     void aboutToOpen(const QString &fileName, const QString &realFileName);
     void openFinishedSuccessfully();