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
private MTrimContribution contribution;
		public TrimKey(MTrimContribution mc) {
			super(mc.getParentId(), mc.getPositionInParent(), mc.getTags(), (MCoreExpression) mc
					.getVisibleWhen());
			this.contribution = mc;
			mc.setWidget(this);
		}
		public MTrimContribution getContribution() {
			return contribution;
		}
	}
	private static MenuKey getKey(MMenuContribution contribution) {
		if (contribution.getWidget() instanceof MenuKey) {
			return (MenuKey) contribution.getWidget();
		}
		return new MenuKey(contribution);
	}
	private static ToolBarKey getKey(MToolBarContribution contribution) {
		if (contribution.getWidget() instanceof ToolBarKey) {