Bug 305739 [viewers] #expandToLevel(Object, level) retrieves all children when virtual
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
if (provider instanceof ILazyTreeContentProvider
				|| provider instanceof ILazyTreePathContentProvider) {
			return;
		}
		super.assertContentProviderType(provider);
	}
	protected Object[] getRawChildren(Object parent) {
		if (contentProviderIsLazy) {
			return new Object[0];
		}
		return super.getRawChildren(parent);
	}
	void preservingSelection(Runnable updateCode, boolean reveal) {
		if (insidePreservingSelection || !getPreserveSelection()){
			
			
			updateCode.run();
			return;
		}
		insidePreservingSelection = true;
		try {
			super.preservingSelection(updateCode, reveal);
		} finally {
			insidePreservingSelection = false;
		}
	}
	/**
	 * For a TreeViewer with a tree with the VIRTUAL style bit set, set the
	 * number of children of the given element or tree path. To set the number
	 * of children of the invisible root of the tree, you can pass the input