src/vs/workbench/api/common/extHostFileSystem.ts/ExtHostFileSystem/$watch
class ExtHostFileSystem:	$watch(handle: number, session: number, resource: UriComponents, opts: files.IWatchOptions): void {
		const subscription = this._getFsProvider(handle).watch(URI.revive(resource), opts);
		this._watches.set(session, subscription);
	}