Bug 328946 Part activation history may return incorrect candidate if no placeholders could be found in a perspective
1. Window > Open Perspective > Other... > CVS Repository Exploring 2. Hide the 'CVS Repositories' view. 3. The 'History' view should become active, it is not.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartActivationHistory.java
}
		generalActivationHistory.remove(part);
		generalActivationHistory.addFirst(part);
	}
	/**
	 * Checks to see if this element and its parents are actually being rendered.
	 */
	private boolean isValid(MUIElement element) {
		if (element == null) {
			return false;
		}
		if (element instanceof MApplication) {
			return true;
		}
		MElementContainer<MUIElement> parent = element.getParent();
		if (parent == null) {
			MPlaceholder placeholder = element.getCurSharedRef();
			if (placeholder == null) {
				return false;
			}
			parent = placeholder.getParent();
			if (parent == null || !placeholder.isToBeRendered() || !placeholder.isVisible()) {
				return false;
			}
		}
		return element.isToBeRendered() && element.isVisible() && isValid(parent);
	}
	/**
	 * Checks to see if this element and its parents are actually being rendered.
	 */