[CP] Plug "temporary leak" when starting new rebuilds before afterContextsCreated is called

[srawlins]

Commit(s) to merge

5e08794

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/c/sdk/+/311520

Issue Description

There is an intermittent ("temporary") memory leak that occurs when the Dart analyzer is rebuilding an "analysis context" (basically any time a pubspec is edited). This CL closes the leak.

What is the fix

The fix is to discard contexts more aggresively.

Why cherry-pick

This issue is a top complaint for users of the analyzer.

Risk

low

Issue link(s)

#52447

Extra Info

No response

[srawlins]

Canceling this cherry-pick; I noticed too late that there is a sizeable merge conflict. Cherry-picking this would, in effect, be writing up a new fix to different files. It is very uncomfortable.

Given that risk, and that this solves a "temporary leak," and that the fix will be released soon in Dart 3.1 anyhow, I'm canceling.