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 MMenuContribution contribution;
		public MenuKey(MMenuContribution mc) {
			super(mc.getParentId(), mc.getPositionInParent(), mc.getTags(), (MCoreExpression) mc
					.getVisibleWhen());
			this.contribution = mc;
			mc.setWidget(this);
		}
		public MMenuContribution getContribution() {
			return contribution;
		}
	}
	static class ToolBarKey extends Key {
		private MToolBarContribution contribution;
		public ToolBarKey(MToolBarContribution mc) {
			super(mc.getParentId(), mc.getPositionInParent(), mc.getTags(), (MCoreExpression) mc
					.getVisibleWhen());
			this.contribution = mc;
			mc.setWidget(this);
		}
		public MToolBarContribution getContribution() {
			return contribution;
		}
	}
	static class TrimKey extends Key {