Update DWDS to handle JS variables that are unavailable in the current scope

[nshahan]

Changes to Chrome DevTools could change the properties visible in a scope or change their value to signal that they are not available. DWDS should be made resilient to these changes as they could come from future V8 optimizations.

[annagrin]

@nshahan can you please give an example?

[nshahan]

@annagrin I left you a comment in an internal doc.

[bkonyi]

@nshahan is this still relevant?

[nshahan]

AFAIK this is a problem that we still haven't dealt with but we are probably more resilient now to avoid crashes. I believe it is similar to the issue seen when debugging on the VM and viewing or evaluating a value in the debugger that the VM has optimized away because it saw no uses in the current scope.

I remember there being some confusion about what variables are shown or missing in the debugger inspector pane.

• Are all Dart variables that should be in scope shown?
• What is displayed when they have been optimized away and the value can't be shown?

Solving this will probably require some investigation into the current state of the features and designing the UI to support values we known should be in scope but are not currently available.