Bug 328339 Part activation history seems to ignore detached windows
1. Detach a view. 2. Drag another view into said detached window. 3. Activate the two views alternatively. 4. Close one of them. 5. A part in the workbench window is activated instead of the other view in the detached window.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartActivationHistory.java
do {
				context.activate();
				context = parent;
				parent = parent.getParent();
			} while (parent.get(MWindow.class) != null);
		}
		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;
			}
		}