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
return false;
		}
		for (MMenuElement item : menuContribution.getChildren()) {
			if (item instanceof MMenu && existingMenuIds.contains(item.getElementId())) {
				
				continue;
			} else if (item instanceof MMenuSeparator
					&& existingSeparatorNames.contains(item.getElementId())) {
				
				continue;
			}
			MMenuElement copy = (MMenuElement) EcoreUtil.copy((EObject) item);
			if (DEBUG) {
				trace("addMenuContribution " + copy, menuModel.getWidget(), menuModel); 
			}
			menuContributionsToRemove.add(copy);
			menuModel.getChildren().add(idx++, copy);
			if (copy instanceof MMenu) {
				existingMenuIds.add(copy.getElementId());
			}
		}
		return true;
	}
	public static boolean processAddition(final MToolBar toolBarModel,
			MToolBarContribution toolBarContribution, List<MToolBarElement> contributions,
			HashSet<String> existingSeparatorNames) {
		int idx = getIndex(toolBarModel, toolBarContribution.getPositionInParent());
		if (idx == -1) {
			return false;
		}