src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeViews/$handleDrop
class ExtHostTreeViews:	async $handleDrop(destinationViewId: string, treeDataTransferDTO: DataTransferDTO, targetItemHandle: string | undefined, token: CancellationToken,
		operationUuid?: string, sourceViewId?: string, sourceTreeItemHandles?: string[]): Promise<void> {
		const treeView = this.treeViews.get(destinationViewId);
		if (!treeView) {
			return Promise.reject(new Error(localize('treeView.notRegistered', 'No tree view with id \'{0}\' registered.', destinationViewId)));
		}

		const treeDataTransfer = DataTransferConverter.toDataTransfer(treeDataTransferDTO);
		if ((sourceViewId === destinationViewId) && sourceTreeItemHandles) {
			await this.addAdditionalTransferItems(treeDataTransfer, treeView, sourceTreeItemHandles, token, operationUuid);
		}
		return treeView.onDrop(treeDataTransfer, targetItemHandle, token);
	}