Expanded variables are collapsed again after every step

[juliandescottes]

From firefox-devtools/devtools-core#744 (where there is already some discussion)

This was reported on the debugger, what would be great is if we could maintain the state. any thoughts on how to do this?

From Bugzilla issue https://bugzilla.mozilla.org/show_bug.cgi?id=1405402

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0
Build ID: 20170926190823

Steps to reproduce:

1. Set breakpoint, run into breakpoint
2. Find object variable, expand it
3. Make single step

Actual results:

Expanded variables are collapsed again

Expected results:

Expanded variables should stay expanded

[juliandescottes]

cc @nchevobbe you had some WIP patches you mentioned in the initial issue, anything new since the issue was closed on devtools-core?

[nchevobbe]

I don't think so. The thing I started working on ended up being complex and we agreed it wasn't a big deal for a given case in the debugger, but I don't think it was this case, which is pretty important.

[jasonLaster]

I think this is a dupe of #3269 which we plan on doing in 64 #6777

[Standard8]

Looks like it, I even commented on that one.... (though someone else will need to close this).