Clear the uniqueId of diff editor when saving

Saving diff editor transforms it to patch-file
read only editor. Clearing the uniqueId
ensures we don't use it anymore for showing
e.g. current file's modifications.

Change-Id: I2010161697bbad254ce1ebe5d0bb6a1f38ae323c
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/coreplugin/editormanager/editormanager.cpp

@@ -2798,6 +2798,11 @@ bool EditorManager::skipOpeningBigTextFile(const QString &filePath)
     return EditorManagerPrivate::skipOpeningBigTextFile(filePath);
 }
 
+void EditorManager::clearUniqueId(IDocument *document)
+{
+    document->setProperty(scratchBufferKey, QVariant());
+}
+
 bool EditorManager::saveDocument(IDocument *document)
 {
     return EditorManagerPrivate::saveDocument(document);

src/plugins/coreplugin/editormanager/editormanager.h

@@ -119,6 +119,7 @@ public:
                                            const QString &uniqueId = QString(),
                                            OpenEditorFlags flags = NoFlags);
     static bool skipOpeningBigTextFile(const QString &filePath);
+    static void clearUniqueId(IDocument *document);
 
     static bool openExternalEditor(const QString &fileName, Id editorId);
     static void addCloseEditorListener(const std::function<bool(IEditor *)> &listener);

src/plugins/diffeditor/diffeditordocument.cpp

@@ -215,6 +215,7 @@ bool DiffEditorDocument::save(QString *errorString, const QString &fileName, boo
 
     setController(0);
     setDescription(QString());
+    Core::EditorManager::clearUniqueId(this);
 
     const QFileInfo fi(fileName);
     setTemporary(false);