src/vs/workbench/browser/parts/editor/editorsObserver.ts/EditorsObserver/onGroupAdded
class EditorsObserver:	private onGroupAdded(group: IEditorGroup): void {

		// Make sure to add any already existing editor
		// of the new group into our list in LRU order
		const groupEditorsMru = group.getEditors(EditorsOrder.MOST_RECENTLY_ACTIVE);
		for (let i = groupEditorsMru.length - 1; i >= 0; i--) {
			this.addMostRecentEditor(group, groupEditorsMru[i], false /* is not active */, true /* is new */);
		}

		// Make sure that active editor is put as first if group is active
		if (this.editorGroupsService.activeGroup === group && group.activeEditor) {
			this.addMostRecentEditor(group, group.activeEditor, true /* is active */, false /* already added before */);
		}

		// Group Listeners
		this.registerGroupListeners(group);
	}