src/vs/workbench/browser/parts/activitybar/activitybarPart.ts/ActivitybarPart/onDidViewContainerVisible
class ActivitybarPart:	private onDidViewContainerVisible(id: string): void {
		const viewContainer = this.getViewContainer(id);
		if (viewContainer) {

			// Update the composite bar by adding
			this.addComposite(viewContainer);
			this.compositeBar.activateComposite(viewContainer.id);

			if (this.shouldBeHidden(viewContainer)) {
				const viewContainerModel = this.viewDescriptorService.getViewContainerModel(viewContainer);
				if (viewContainerModel.activeViewDescriptors.length === 0) {
					// Update the composite bar by hiding
					this.hideComposite(viewContainer.id);
				}
			}
		}
	}