Bug 318713 Duplicate toolbar items (navigate group)
SDK 4.0 - I20100701-1105. 1. start fresh workspace ==> navigate group appears twice which is quite confusing and wastes space.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ContributionsAnalyzer.java
boolean popup = parentID.equals(POPUP_PARENT_ID) && (menuModel instanceof MPopupMenu)
					&& includePopups;
			boolean filtered = isFiltered(menuModel, menuContribution);
			if (filtered || (!popup && !parentID.equals(id)) || !menuContribution.isToBeRendered()) {
				continue;
			}
			if (menuBar || isVisible(menuContribution, eContext)) {
				toContribute.add(menuContribution);
			}
		}
	}
	static boolean isFiltered(MMenu menuModel, MMenuContribution menuContribution) {
		if (menuModel.getTags().contains(ContributionsAnalyzer.MC_POPUP)) {
			return !menuContribution.getTags().contains(ContributionsAnalyzer.MC_POPUP)
					&& menuContribution.getTags().contains(ContributionsAnalyzer.MC_MENU);
		}
		if (menuModel.getTags().contains(ContributionsAnalyzer.MC_MENU)) {
			return !menuContribution.getTags().contains(ContributionsAnalyzer.MC_MENU)
					&& menuContribution.getTags().contains(ContributionsAnalyzer.MC_POPUP);
		}
		return false;
	}
	public static boolean isVisible(MMenuContribution menuContribution, ExpressionContext eContext) {
		if (menuContribution.getVisibleWhen() == null) {
			return true;
		}
		return isVisible((MCoreExpression) menuContribution.getVisibleWhen(), eContext);
	}
	public static boolean isVisible(MToolBarContribution contribution, ExpressionContext eContext) {
		if (contribution.getVisibleWhen() == null) {