Bug 81983 [preferences] Disabling and enabling folding on small file takes forever
3.1 M4 Using enable/disable folding on a small CU takes forever. This is caused by the recent change to apply the preference to all Java editors. In another (hidden) window (Debug) I had StyledText open which (understandably) took long to react on the preference change. Non-visible editor's should not react to this change until they become visible.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
segments= result;
		}
		
		return segments;
	}
		
	/**
	 * Returns a segmentation of the given line appropriate for BIDI rendering. The default
	 * implementation returns only the string literals of a java code line as segments.
	 * 
	 * @param widgetLineOffset the offset of the line
	 * @param line the content of the line
	 * @return the line's BIDI segmentation
	 */
	protected int[] getBidiLineSegments(int widgetLineOffset, String line) {
		if (line != null && line.length() > 0) {
			ISourceViewer sourceViewer= getSourceViewer();
			if (sourceViewer != null) {
				int lineOffset;
				if (sourceViewer instanceof ITextViewerExtension5) {
					ITextViewerExtension5 extension= (ITextViewerExtension5) sourceViewer;
					lineOffset= extension.widgetOffset2ModelOffset(widgetLineOffset);
				} else {
					IRegion visible= sourceViewer.getVisibleRegion();
					lineOffset= visible.getOffset() + widgetLineOffset;
				}
				try {
					return getBidiLineSegments(sourceViewer, lineOffset);
				} catch (BadLocationException x) {