Don't show Design mode if "designer" plugins are disabled/not present.

Change-Id: Iee0a01491075e1e82c17211b5e119bd5e167763b
Reviewed-by: Marco Bubke <marco.bubke@nokia.com>

src/plugins/coreplugin/designmode.cpp

@@ -54,6 +54,8 @@
 #include <QtGui/QPlainTextEdit>
 #include <QtGui/QStackedWidget>
 
+static Core::DesignMode *m_instance = 0;
+
 namespace Core {
 
 class EditorManager;
@@ -103,6 +105,7 @@ public:
     Internal::DesignModeCoreListener *m_coreListener;
     QWeakPointer<Core::IEditor> m_currentEditor;
     bool m_isActive;
+    bool m_isRequired;
     QList<DesignEditorInfo*> m_editors;
     QStackedWidget *m_stackWidget;
     Context m_activeContext;
@@ -111,6 +114,7 @@ public:
 DesignModePrivate::DesignModePrivate(DesignMode *q)
   : m_coreListener(new Internal::DesignModeCoreListener(q)),
     m_isActive(false),
+    m_isRequired(false),
     m_stackWidget(new QStackedWidget)
 {
 }
@@ -118,6 +122,7 @@ DesignModePrivate::DesignModePrivate(DesignMode *q)
 DesignMode::DesignMode()
     : d(new DesignModePrivate(this))
 {
+    m_instance = this;
     setObjectName(QLatin1String("DesignMode"));
     setEnabled(false);
     setContext(Context(Constants::C_DESIGN_MODE));
@@ -146,6 +151,21 @@ DesignMode::~DesignMode()
     delete d;
 }
 
+DesignMode *DesignMode::instance()
+{
+    return m_instance;
+}
+
+void DesignMode::setDesignModeIsRequired()
+{
+    d->m_isRequired = true;
+}
+
+bool DesignMode::designModeIsRequired() const
+{
+    return d->m_isRequired;
+}
+
 QStringList DesignMode::registeredMimeTypes() const
 {
     QStringList rc;
@@ -163,6 +183,7 @@ void DesignMode::registerDesignWidget(QWidget *widget,
                                       const QStringList &mimeTypes,
                                       const Context &context)
 {
+    setDesignModeIsRequired();
     int index = d->m_stackWidget->addWidget(widget);
 
     DesignEditorInfo *info = new DesignEditorInfo;