CorePlugin: Use static VariableManager functions where appropriate

Change-Id: Ie3d34a829522e15b2a56c0fcc696e60163a9be32
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/coreplugin/editormanager/editormanager.cpp

@@ -2520,7 +2520,7 @@ QString EditorManager::windowTitleVcsTopic()
 
 void EditorManager::updateVariable(const QByteArray &variable)
 {
-    if (VariableManager::instance()->isFileVariable(variable, kCurrentDocumentPrefix)) {
+    if (VariableManager::isFileVariable(variable, kCurrentDocumentPrefix)) {
         QString value;
         IDocument *document = currentDocument();
         if (document) {

src/plugins/coreplugin/variablemanager.cpp

@@ -276,7 +276,7 @@ Utils::AbstractMacroExpander *VariableManager::macroExpander()
  * Returns the variable manager instance, for connecting to signals. All other methods are static
  * and should be called as class methods, not through the instance.
  */
-VariableManager *VariableManager::instance()
+QObject *VariableManager::instance()
 {
     return variableManagerInstance;
 }

src/plugins/coreplugin/variablemanager.h

@@ -50,7 +50,7 @@ class CORE_EXPORT VariableManager : public QObject
     Q_OBJECT
 
 public:
-    static VariableManager *instance();
+    static QObject *instance();
 
     static void insert(const QByteArray &variable, const QString &value);
     static bool remove(const QByteArray &variable);

src/plugins/qtsupport/qtsupportplugin.cpp

@@ -117,18 +117,18 @@ void QtSupportPlugin::updateVariable(const QByteArray &variable)
 
     ProjectExplorer::Project *project = ProjectExplorer::ProjectExplorerPlugin::currentProject();
     if (!project || !project->activeTarget()) {
-        Core::VariableManager::instance()->remove(variable);
+        Core::VariableManager::remove(variable);
         return;
     }
 
     const BaseQtVersion *qtVersion = QtKitInformation::qtVersion(project->activeTarget()->kit());
     if (!qtVersion) {
-        Core::VariableManager::instance()->remove(variable);
+        Core::VariableManager::remove(variable);
         return;
     }
 
     QString value = qtVersion->qmakeProperty(variable == kHostBins ? "QT_HOST_BINS" : "QT_INSTALL_BINS");
-    Core::VariableManager::instance()->insert(variable, value);
+    Core::VariableManager::insert(variable, value);
 }
 
 Q_EXPORT_PLUGIN(QtSupportPlugin)