Implement assert() messages behind a flag in analyzer

[munificent]

This is the analyzer-specific issue for #24213. That issue has the details.

[stereotype441]

https://codereview.chromium.org/1309543011/ adds support to the analysis engine. Once that has been reviewed and landed, we will need to make a separate (trivial) changes to analyzer_cli and analysis_server to add the flag.

[sethladd]

Thanks!

Should I open a new issue to track the other plumbing?

Update: I just did :)

[munificent]

And you added tests. 🤘

[sethladd]

The DEP met today, and decided that the type annotation on the optional param should be String. Does the CL reflect that?

[stereotype441]

IIRC, the CL does reflect that. However I can't verify right now since codereview.chromium.org appears to be down due to certificate errors. I will check back tomorrow to confirm.

[sethladd]

Thanks Paul.

[stereotype441]

I just double-checked, and yes, the CL is consistent with the proposed spec change. It requires the optional assertion message param to be assignable to String, or a warning is issued.

[sethladd]

Thanks @stereotype441 for checking!

[bwilkerson]

Messages in asserts is now enabled by default in analyzer (https://codereview.chromium.org/2557513008/).