Teach web_sdk/sdk_rewritter.dart how to write a stamp file.

[eseidel]

Description

Previously BUILD.gn expected a stamp, but one was never generated.
This meant that the null build for the engine was always
rebuilding the 7 targets for the web_sdk.

This adds a --stamp option to sdk_rewritter and changes the
BUILD.gn file to use it, following the pattern for --stamp
options seen throughout the chromium codebase.

Related Issues

Fixes flutter/flutter#59720

Tests

There were no existing tests for sdk_rewritter.dart, and I didn't write any. :(

Checklist

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• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.
  (Realistically, please just revert if this breaks.)

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.
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[fluttergithubbot]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[eseidel]

I welcome pointers on how scripts like this should be tests (happy to write them). @jonahwilliams @nturgut

[jonahwilliams]

If it builds...

[jonahwilliams]

LGTM

[eseidel]

I thought we had a fancy commit queue now? https://github.com/flutter/flutter/wiki/Tree-hygiene#landing-a-patch doesn't mention such.

Is there a button I have to press to get it into the landing queue (assuming such exists)? Thanks!

[jonahwilliams]

I think it is automatic now - the github status now include LUCI checks automagically!

[eseidel]

Is there more I need to do?

[jonahwilliams]

you gotta press submit :)

[eseidel]

This normal-human account doesn't have any privileges (which is part of the point). Is there no way to get into the submission queue without them (e.g. for someone else to put this in the queue)?

I just see a "Only those with write access to this repository can merge pull requests".

[jonahwilliams]

I guess I gotta put the label on it! It should get merged whenever the bot feels like it