src/vs/workbench/browser/parts/activitybar/activitybarPart.ts/ActivitybarPart/onDidRegisterViewContainers
class ActivitybarPart:	private onDidRegisterViewContainers(viewContainers: readonly ViewContainer[]): void {
		for (const viewContainer of viewContainers) {
			this.addComposite(viewContainer);

			// Pin it by default if it is new
			const cachedViewContainer = this.cachedViewContainers.filter(({ id }) => id === viewContainer.id)[0];
			if (!cachedViewContainer) {
				this.compositeBar.pin(viewContainer.id);
			}

			// Active
			const visibleViewContainer = this.paneCompositePart.getActivePaneComposite();
			if (visibleViewContainer?.getId() === viewContainer.id) {
				this.compositeBar.activateComposite(viewContainer.id);
			}

			const viewContainerModel = this.viewDescriptorService.getViewContainerModel(viewContainer);
			this.updateActivity(viewContainer, viewContainerModel);
			this.showOrHideViewContainer(viewContainer);

			const disposables = new DisposableStore();
			disposables.add(viewContainerModel.onDidChangeContainerInfo(() => this.updateActivity(viewContainer, viewContainerModel)));
			disposables.add(viewContainerModel.onDidChangeActiveViewDescriptors(() => this.showOrHideViewContainer(viewContainer)));

			this.viewContainerDisposables.set(viewContainer.id, disposables);
		}
	}