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
uninstallOccurrencesFinder();
		
		uninstallOverrideIndicator();
		
		uninstallSemanticHighlighting();
		
		if (fActivationListener != null) {
			Shell shell= getEditorSite().getShell();
			if (shell != null && !shell.isDisposed())
				shell.removeShellListener(fActivationListener);
			fActivationListener= null;
		}
		
		if (fEncodingSupport != null) {
			fEncodingSupport.dispose();
			fEncodingSupport= null;
		}
		
		if (fBracketMatcher != null) {
			fBracketMatcher.dispose();
			fBracketMatcher= null;
		}
		
		if (fSelectionHistory != null) {
			fSelectionHistory.dispose();
			fSelectionHistory= null;
		}
		
		if (fEditorSelectionChangedListener != null)  {
			fEditorSelectionChangedListener.uninstall(getSelectionProvider());