src/vs/platform/files/browser/indexedDBFileSystemProvider.ts/IndexedDBFileSystemProvider/readFile
class IndexedDBFileSystemProvider:	async readFile(resource: URI): Promise<Uint8Array> {
		const buffer = await new Promise<Uint8Array>((c, e) => {
			const transaction = this.database.transaction([this.store]);
			transaction.oncomplete = () => {
				if (request.result instanceof Uint8Array) {
					c(request.result);
				} else if (typeof request.result === 'string') {
					c(VSBuffer.fromString(request.result).buffer);
				}
				else {
					if (request.result === undefined) {
						e(ERR_FILE_NOT_FOUND);
					} else {
						e(ERR_UNKNOWN_INTERNAL(`IndexedDB entry at "${resource.path}" in unexpected format`));
					}
				}
			};
			transaction.onerror = () => e(transaction.error);

			const objectStore = transaction.objectStore(this.store);
			const request = objectStore.get(resource.path);
		});

		(await this.getFiletree()).add(resource.path, { type: 'file', size: buffer.byteLength });
		return buffer;
	}