[State Restoration] Navigator assert on non restorable routes returned by onGenerateInitialRoutes

[shihaohong]

Description

Fixes #72453.

However, I'm running into trouble writing the test. The expect statements catch the new assert I added, but there is another unrelated assert that throws somehow after the test function body is done executing, and I'm not sure how to catch it or stop it from happening. I've tried adding and awaiting widget pump, pumpAndSettle, even pumpWidget at the end of the test function, but I'm not sure what's going on and at this point I'm just trying random things to make the assert go away:

00:05 +29: Helpful assert thrown all routes in onGenerateInitialRoutes are not restorable                                        
══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following assertion was thrown attaching to the render tree:
'package:flutter/src/widgets/framework.dart': Failed assertion: line 5150 pos 14:
'_dependents.isEmpty': is not true.

Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=2_bug.md

When the exception was thrown, this was the stack:
#2      InheritedElement.debugDeactivated.<anonymous closure> (package:flutter/src/widgets/framework.dart:5150:14)
#3      InheritedElement.debugDeactivated (package:flutter/src/widgets/framework.dart:5152:6)
#4      _InactiveElements._deactivateRecursively.<anonymous closure> (package:flutter/src/widgets/framework.dart:2044:15)
#5      _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2046:6)
#6      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#7      _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#8      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#9      _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#10     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#11     _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#12     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#13     _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#14     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#15     _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#16     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#17     _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#18     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:4735:14)
#19     _InactiveElements._deactivateRecursively (package:flutter/src/widgets/framework.dart:2042:13)
#20     _InactiveElements.add (package:flutter/src/widgets/framework.dart:2054:7)
#21     Element.deactivateChild (package:flutter/src/widgets/framework.dart:3657:30)
#22     Element.updateChild (package:flutter/src/widgets/framework.dart:3381:9)
#23     RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1208:16)
#24     RenderObjectToWidgetElement.update (package:flutter/src/widgets/binding.dart:1186:5)
#25     RenderObjectToWidgetElement.performRebuild (package:flutter/src/widgets/binding.dart:1200:7)
#26     Element.rebuild (package:flutter/src/widgets/framework.dart:4375:5)
#27     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2774:33)
#28     AutomatedTestWidgetsFlutterBinding.drawFrame (package:flutter_test/src/binding.dart:1110:19)
#29     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:320:5)
#30     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1144:15)
#31     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1082:9)
#32     AutomatedTestWidgetsFlutterBinding.scheduleWarmUpFrame (package:flutter_test/src/binding.dart:1056:5)
#33     runApp (package:flutter/src/widgets/binding.dart:1049:7)
#34     TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:804:7)
<asynchronous suspension>
(elided 2 frames from class _AssertionError)
════════════════════════════════════════════════════════════════════════════════════════════════════
00:05 +29 -1: Helpful assert thrown all routes in onGenerateInitialRoutes are not restorable [E]                                 
  Test failed. See exception logs above.
  The test description was: Helpful assert thrown all routes in onGenerateInitialRoutes are not restorable

Checklist

Before you create this PR, confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.
  • I wrote a design doc: https://flutter.dev/go/template Replace this with a link to your design doc's short link
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: https://flutter.dev/go/breaking-changes-template Replace this with a link to a pull request that adds the migration guide to https://flutter.dev/docs/release/breaking-changes

[chunhtai]

This is due to the tree is left half broken and the test fail to tear it down. I remember I ran into this issue before, and the way i do it is to make sure the tree is restored before the test ends

[chunhtai]

LGTM, modulo nits and failing test

[chunhtai]

Suggested change

	'Please make sure that all routes returned in onGenerateInitialRoutes '
	'Please make sure that all routes returned from the onGenerateInitialRoutes '

[chunhtai]

Suggested change

	'have their RouteSettings defined with a name that is defined in the '
	'have their RouteSettings defined with names that are defined in the '