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
if (JavaCore.COMPILER_SOURCE.equals(property)) {
				if (event.getNewValue() instanceof String)
					fBracketMatcher.setSourceVersion((String) event.getNewValue());
				
			}
			
			((JavaSourceViewerConfiguration)getSourceViewerConfiguration()).handlePropertyChangeEvent(event);
			
			if (affectsOverrideIndicatorAnnotations(event)) {
				if (isShowingOverrideIndicators()) {
					if (fOverrideIndicatorManager == null)
						installOverrideIndicator(true);
				} else {
					if (fOverrideIndicatorManager != null)
						uninstallOverrideIndicator();
				}
				return;
			}
			
			if (PreferenceConstants.EDITOR_FOLDING_PROVIDER.equals(property)) {
				if (sourceViewer instanceof ProjectionViewer) {
					ProjectionViewer projectionViewer= (ProjectionViewer) sourceViewer;
					if (fProjectionModelUpdater != null)
						fProjectionModelUpdater.uninstall();
					
					fProjectionModelUpdater= JavaPlugin.getDefault().getFoldingStructureProviderRegistry().getCurrentFoldingProvider();
					if (fProjectionModelUpdater != null) {
						fProjectionModelUpdater.install(this, projectionViewer);
					}