extensions/git/src/fileSystemProvider.ts/GitFileSystemProvider/cleanup
class GitFileSystemProvider:	private cleanup(): void {
		const now = new Date().getTime();
		const cache = new Map<string, CacheRow>();

		for (const row of this.cache.values()) {
			const { path } = fromGitUri(row.uri);
			const isOpen = workspace.textDocuments
				.filter(d => d.uri.scheme === 'file')
				.some(d => pathEquals(d.uri.fsPath, path));

			if (isOpen || now - row.timestamp < THREE_MINUTES) {
				cache.set(row.uri.toString(), row);
			} else {
				// TODO: should fire delete events?
			}
		}

		this.cache = cache;
	}