src/vs/workbench/common/views.ts/ViewsRegistry/addViews
class ViewsRegistry:	private addViews(viewDescriptors: IViewDescriptor[], viewContainer: ViewContainer): void {
		let views = this._views.get(viewContainer);
		if (!views) {
			views = [];
			this._views.set(viewContainer, views);
			this._viewContainers.push(viewContainer);
		}
		for (const viewDescriptor of viewDescriptors) {
			if (this.getView(viewDescriptor.id) !== null) {
				throw new Error(localize('duplicateId', "A view with id '{0}' is already registered", viewDescriptor.id));
			}
			views.push(viewDescriptor);
		}
	}