src/vs/workbench/browser/parts/views/viewPaneContainer.ts/ViewPaneContainer/addPanes
class ViewPaneContainer:	addPanes(panes: { pane: ViewPane, size: number, index?: number; }[]): void {
		const wasMerged = this.isViewMergedWithContainer();

		for (const { pane: pane, size, index } of panes) {
			this.addPane(pane, size, index);
		}

		this.updateViewHeaders();
		if (this.isViewMergedWithContainer() !== wasMerged) {
			this.updateTitleArea();
		}

		this._onDidAddViews.fire(panes.map(({ pane }) => pane));
	}