src/vs/platform/files/common/inMemoryFilesystemProvider.ts/InMemoryFileSystemProvider/writeFile
class InMemoryFileSystemProvider:	async writeFile(resource: URI, content: Uint8Array, opts: IFileWriteOptions): Promise<void> {
		const basename = resources.basename(resource);
		const parent = this._lookupParentDirectory(resource);
		let entry = parent.entries.get(basename);
		if (entry instanceof Directory) {
			throw new FileSystemProviderError('file is directory', FileSystemProviderErrorCode.FileIsADirectory);
		}
		if (!entry && !opts.create) {
			throw new FileSystemProviderError('file not found', FileSystemProviderErrorCode.FileNotFound);
		}
		if (entry && opts.create && !opts.overwrite) {
			throw new FileSystemProviderError('file exists already', FileSystemProviderErrorCode.FileExists);
		}
		if (!entry) {
			entry = new File(basename);
			parent.entries.set(basename, entry);
			this._fireSoon({ type: FileChangeType.ADDED, resource });
		}
		entry.mtime = Date.now();
		entry.size = content.byteLength;
		entry.data = content;

		this._fireSoon({ type: FileChangeType.UPDATED, resource });
	}