Commit(s) to merge

82520ab and 84b38ae

Target

stable and beta

Prepared changelist for beta/stable

stable - https://dart-review.googlesource.com/c/sdk/+/347650
beta - https://dart-review.googlesource.com/c/sdk/+/347760

Issue Description

The change fixes the following

• an issue that causes Flutter apps to freeze when breakpoints are added to multiple isolates at the same time
• an issue that causes Flutter apps to crash during hot reload

What is the fix

• Use safepoint-safe RwLock for breakpoint locations locks
• Ensure setting breakpoints is lock-safe

Why cherry-pick

Flutter app developers have encountered these scenarios effecting developer productivity.

Risk

low

Issue link(s)

#54650
flutter/flutter#140878

Extra Info

No response