Add sizeChanged signal for composer item

src/core/composer/qgscomposeritem.cpp

@@ -724,6 +724,8 @@ void QgsComposerItem::setSceneRect( const QRectF& rectangle )
   QTransform t;
   t.translate( xTranslation, yTranslation );
   setTransform( t );
+
+  emit sizeChanged();
 }
 
 void QgsComposerItem::drawBackground( QPainter* p )

src/core/composer/qgscomposeritem.h

@@ -351,6 +351,8 @@ class CORE_EXPORT QgsComposerItem: public QObject, public QGraphicsRectItem
     void rotationChanged( double newRotation );
     /**Used e.g. by the item widgets to update the gui elements*/
     void itemChanged();
+    /**Emitted if the rectangle changes*/
+    void sizeChanged();
   private:
     // Label id (unique within the same composition)
     QString mId;