Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
|| key.equals(preference.getTextPreferenceKey());
	}
	/**
	 * @return <code>true</code> if Semantic Highlighting is enabled.
	 * 
	 * @since 3.0
	 */
	private boolean isSemanticHighlightingEnabled() {
		return getPreferenceStore().getBoolean(PreferenceConstants.EDITOR_SEMANTIC_HIGHLIGHTING_ENABLED);
	}
	
	/**
	 * Install Semantic Highlighting.
	 * 
	 * @since 3.0
	 */
	private void installSemanticHighlighting() {
		if (fSemanticManager == null) {
			fSemanticManager= new SemanticHighlightingManager();
			fSemanticManager.install(this, (JavaSourceViewer) getSourceViewer(), JavaPlugin.getDefault().getJavaTextTools().getColorManager(), getPreferenceStore());
		}
	}
	
	/**
	 * Uninstall Semantic Highlighting.
	 * 
	 * @since 3.0
	 */
	private void uninstallSemanticHighlighting() {
		if (fSemanticManager != null) {