Bug 28698 Ctrl+O (show outline) does not work if the file being shown in the editor is read only
M4 The summary tells all. Works if the file is not read only. Is this by design?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
protected void layout(Composite composite, boolean flushCache) {
			Rectangle clArea= composite.getClientArea();
			if (fAdaptedSourceViewer.isVerticalRulerVisible()) {
				
				StyledText textWidget= fAdaptedSourceViewer.getTextWidget();
				Rectangle trim= textWidget.computeTrim(0, 0, 0, 0);
				int scrollbarHeight= trim.height;
				
				IVerticalRuler vr= fAdaptedSourceViewer.getVerticalRuler();
				int vrWidth=vr.getWidth();
				
				int orWidth= 0;
				if (fAdaptedSourceViewer.isOverviewRulerVisible()) {
					OverviewRuler or= fAdaptedSourceViewer.getOverviewRuler();
					orWidth= or.getWidth();
					or.getControl().setBounds(clArea.width - orWidth, scrollbarHeight, orWidth, clArea.height - 3*scrollbarHeight);
				}
				
				textWidget.setBounds(vrWidth + fGap, 0, clArea.width - vrWidth - orWidth - 2*fGap, clArea.height);
				vr.getControl().setBounds(0, 0, vrWidth, clArea.height - scrollbarHeight);
				
			} else {
				StyledText textWidget= fAdaptedSourceViewer.getTextWidget();
				textWidget.setBounds(0, 0, clArea.width, clArea.height);
			}
		}
	};
	
	class AdaptedSourceViewer extends JavaCorrectionSourceViewer  {