src/vs/workbench/api/common/extHostCustomEditors.ts/ExtHostCustomEditors/$onSave
class ExtHostCustomEditors:	async $onSave(resourceComponents: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void> {
		const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
		const provider = this.getCustomEditorProvider(viewType);
		await provider.saveCustomDocument(entry.document, cancellation);
		entry.disposeBackup();
	}