src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeViews/$onDrop
class ExtHostTreeViews:	$onDrop(treeViewId: string, treeItemHandles: string[], newParentItemHandle: string): Promise<void> {
		const treeView = this.treeViews.get(treeViewId);
		if (!treeView) {
			return Promise.reject(new Error(localize('treeView.notRegistered', 'No tree view with id \'{0}\' registered.', treeViewId)));
		}
		return treeView.onDrop(treeItemHandles, newParentItemHandle);
	}