src/vs/workbench/browser/parts/editor/editorGroupView.ts/EditorGroupView/pinEditor
class EditorGroupView:	pinEditor(candidate: EditorInput | undefined = this.activeEditor || undefined): void {
		if (candidate && !this.model.isPinned(candidate)) {

			// Update model
			const editor = this.model.pin(candidate);

			// Forward to title control
			if (editor) {
				this.titleAreaControl.pinEditor(editor);
			}
		}
	}