Workaround for iOS rewinddir issue

[liyuqian]

Fixes flutter/flutter#65258

The following devicelab tests should pass after this patch:

• flutter_gallery_sksl_warmup__transition_perf_e2e_ios32
• flutter_gallery_sksl_warmup_ios32__transition_perf

[flutter-dashboard]

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[jason-simmons]

What is the behavior of rewinddir when it fails?

If calling rewinddir on the duped directory file descriptor is unreliable on some platforms, then would it be worthwhile to create a version of VisitFiles that takes a directory path instead of an FD?

[liyuqian]

I don't see anything when it fails. There's no return value or error defined according to this doc.

As for taking a directory path, currently we don't have a unified way of getting that path. In some cases, we use GetCachesDirectory and let the platform return an arbitrary directory without giving us a path. It seems that unless the directory is invalid, we can always get a string path representation. Do you think it's a good idea to add a std::string GetCachesDirectoryPath() function that returns a valid path or an empty string on all platforms?

[jason-simmons]

I'd like to get a better understanding of what happens when rewinddir isn't working as expected.

But if rewinddir is broken, then I'd rather add the GetCachesDirectoryPath function and a path-based VisitFiles instead of having an FD-based VisitFiles that doesn't work reliably.

[liyuqian]

@jason-simmons : it turns out that we don't need to open from the root directory. Just reopen the last sub-directory is enough so the fix could be very short. I'm closing this PR in favor of #21050.