Give file system recording serialization a timeout. (#15217)

Some file I/O is piped from OS processes and never completes,
so without havign a timeout on the recording serialzation, we
end up waiting forever on that I/O to complete.

packages/flutter_tools/lib/src/base/file_system.dart

@@ -7,7 +7,6 @@ import 'package:file/local.dart';
 import 'package:file/memory.dart';
 import 'package:file/record_replay.dart';
 
-
 import 'common.dart' show throwToolExit;
 import 'context.dart';
 import 'platform.dart';
@@ -40,7 +39,9 @@ void enableRecordingFileSystem(String location) {
   final RecordingFileSystem fileSystem = new RecordingFileSystem(
       delegate: _kLocalFs, destination: dir);
   addShutdownHook(() async {
-    await fileSystem.recording.flush();
+    await fileSystem.recording.flush(
+      pendingResultTimeout: const Duration(seconds: 5),
+    );
     context.setVariable(FileSystem, originalFileSystem);
   }, ShutdownStage.SERIALIZE_RECORDING);
   context.setVariable(FileSystem, fileSystem);

packages/flutter_tools/lib/src/base/process.dart

@@ -26,10 +26,10 @@ typedef Future<dynamic> ShutdownHook();
 /// a given stage will be started in parallel and will be guaranteed to run to
 /// completion before shutdown hooks in the next stage are started.
 class ShutdownStage implements Comparable<ShutdownStage> {
-  const ShutdownStage._(this._priority);
+  const ShutdownStage._(this.priority);
 
   /// The stage priority. Smaller values will be run before larger values.
-  final int _priority;
+  final int priority;
 
   /// The stage before the invocation recording (if one exists) is serialized
   /// to disk. Tasks performed during this stage *will* be recorded.
@@ -48,7 +48,7 @@ class ShutdownStage implements Comparable<ShutdownStage> {
   static const ShutdownStage CLEANUP = const ShutdownStage._(4);
 
   @override
-  int compareTo(ShutdownStage other) => _priority.compareTo(other._priority);
+  int compareTo(ShutdownStage other) => priority.compareTo(other.priority);
 }
 
 Map<ShutdownStage, List<ShutdownHook>> _shutdownHooks = <ShutdownStage, List<ShutdownHook>>{};
@@ -75,9 +75,11 @@ void addShutdownHook(
 /// guaranteed to run to completion before shutdown hooks in the next stage are
 /// started.
 Future<Null> runShutdownHooks() async {
+  printTrace('Running shutdown hooks');
   _shutdownHooksRunning = true;
   try {
     for (ShutdownStage stage in _shutdownHooks.keys.toList()..sort()) {
+      printTrace('Shutdown hook priority ${stage.priority}');
       final List<ShutdownHook> hooks = _shutdownHooks.remove(stage);
       final List<Future<dynamic>> futures = <Future<dynamic>>[];
       for (ShutdownHook shutdownHook in hooks)
@@ -88,6 +90,7 @@ Future<Null> runShutdownHooks() async {
     _shutdownHooksRunning = false;
   }
   assert(_shutdownHooks.isEmpty);
+  printTrace('Shutdown hooks complete');
 }
 
 Map<String, String> _environment(bool allowReentrantFlutter, [Map<String, String> environment]) {

packages/flutter_tools/test/base/process_test.dart

@@ -5,9 +5,11 @@
 import 'package:flutter_tools/src/base/process.dart';
 import 'package:test/test.dart';
 
+import '../src/context.dart';
+
 void main() {
   group('shutdownHooks', () {
-    test('runInExpectedOrder', () async {
+    testUsingContext('runInExpectedOrder', () async {
       int i = 1;
       int serializeRecording1;
       int serializeRecording2;