Auto merge of #18548 - nnethercote:measure-smallbitvec, r=emilio
Auto merge of #18548 - nnethercote:measure-smallbitvec, r=emilio

Implement MallocSizeOf properly for SmallBitVec.

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because: trivial, and tested on Gecko side.

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/18548)
<!-- Reviewable:end -->

DominoTree/servo,dsandeephegde/servo,saneyuki/servo,thiagopnts/servo,notriddle/servo,canaltinova/servo,saneyuki/servo,dsandeephegde/servo,SimonSapin/servo,peterjoel/servo,thiagopnts/servo,canaltinova/servo,emilio/servo,emilio/servo,anthgur/servo,cbrewster/servo,nnethercote/servo,thiagopnts/servo,sadmansk/servo,avadacatavra/servo,DominoTree/servo,cbrewster/servo,mbrubeck/servo,DominoTree/servo,mbrubeck/servo,upsuper/servo,mattnenterprise/servo,splav/servo,emilio/servo,sadmansk/servo,KiChjang/servo,paulrouget/servo,anthgur/servo,notriddle/servo,szeged/servo,DominoTree/servo,DominoTree/servo,fiji-flo/servo,CJ8664/servo,sadmansk/servo,saneyuki/servo,nnethercote/servo,jimberlage/servo,pyfisch/servo,dsandeephegde/servo,jimberlage/servo,CJ8664/servo,dati91/servo,mattnenterprise/servo,rnestler/servo,jimberlage/servo,pyfisch/servo,szeged/servo,szeged/servo,DominoTree/servo,ConnorGBrewster/servo,larsbergstrom/servo,KiChjang/servo,pyfisch/servo,KiChjang/servo,mbrubeck/servo,sadmansk/servo,nnethercote/servo,DominoTree/servo,cbrewster/servo,upsuper/servo,cbrewster/servo,CJ8664/servo,dsandeephegde/servo,eddyb/servo,thiagopnts/servo,mbrubeck/servo,upsuper/servo,CJ8664/servo,jimberlage/servo,dati91/servo,anthgur/servo,notriddle/servo,splav/servo,paulrouget/servo,cbrewster/servo,splav/servo,peterjoel/servo,sadmansk/servo,eddyb/servo,canaltinova/servo,pyfisch/servo,larsbergstrom/servo,anthgur/servo,emilio/servo,larsbergstrom/servo,splav/servo,emilio/servo,SimonSapin/servo,szeged/servo,larsbergstrom/servo,upsuper/servo,cbrewster/servo,larsbergstrom/servo,jimberlage/servo,nnethercote/servo,dsandeephegde/servo,peterjoel/servo,paulrouget/servo,ConnorGBrewster/servo,eddyb/servo,upsuper/servo,szeged/servo,szeged/servo,avadacatavra/servo,upsuper/servo,KiChjang/servo,ConnorGBrewster/servo,fiji-flo/servo,avadacatavra/servo,peterjoel/servo,pyfisch/servo,peterjoel/servo,peterjoel/servo,KiChjang/servo,emilio/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,nnethercote/servo,KiChjang/servo,larsbergstrom/servo,eddyb/servo,nnethercote/servo,emilio/servo,dati91/servo,pyfisch/servo,emilio/servo,szeged/servo,pyfisch/servo,pyfisch/servo,larsbergstrom/servo,pyfisch/servo,CJ8664/servo,paulrouget/servo,thiagopnts/servo,CJ8664/servo,mbrubeck/servo,pyfisch/servo,saneyuki/servo,eddyb/servo,larsbergstrom/servo,nnethercote/servo,notriddle/servo,mbrubeck/servo,fiji-flo/servo,splav/servo,paulrouget/servo,emilio/servo,notriddle/servo,peterjoel/servo,mattnenterprise/servo,ConnorGBrewster/servo,eddyb/servo,canaltinova/servo,saneyuki/servo,paulrouget/servo,peterjoel/servo,mbrubeck/servo,mattnenterprise/servo,canaltinova/servo,canaltinova/servo,paulrouget/servo,mattnenterprise/servo,avadacatavra/servo,splav/servo,dsandeephegde/servo,DominoTree/servo,avadacatavra/servo,saneyuki/servo,ConnorGBrewster/servo,cbrewster/servo,dati91/servo,notriddle/servo,mattnenterprise/servo,rnestler/servo,avadacatavra/servo,thiagopnts/servo,nnethercote/servo,anthgur/servo,jimberlage/servo,cbrewster/servo,jimberlage/servo,jimberlage/servo,CJ8664/servo,emilio/servo,KiChjang/servo,szeged/servo,sadmansk/servo,fiji-flo/servo,sadmansk/servo,fiji-flo/servo,rnestler/servo,SimonSapin/servo,splav/servo,sadmansk/servo,eddyb/servo,dati91/servo,paulrouget/servo,thiagopnts/servo,jimberlage/servo,KiChjang/servo,mbrubeck/servo,rnestler/servo,dsandeephegde/servo,SimonSapin/servo,rnestler/servo,anthgur/servo,dati91/servo,eddyb/servo,anthgur/servo,CJ8664/servo,upsuper/servo,fiji-flo/servo,canaltinova/servo,fiji-flo/servo,DominoTree/servo,saneyuki/servo,anthgur/servo,canaltinova/servo,rnestler/servo,dati91/servo,avadacatavra/servo,peterjoel/servo,saneyuki/servo,splav/servo,larsbergstrom/servo,saneyuki/servo,paulrouget/servo,SimonSapin/servo,saneyuki/servo,nnethercote/servo,upsuper/servo,mattnenterprise/servo,szeged/servo,KiChjang/servo,peterjoel/servo,notriddle/servo,larsbergstrom/servo,dati91/servo,avadacatavra/servo,SimonSapin/servo,ConnorGBrewster/servo,thiagopnts/servo,splav/servo,DominoTree/servo,szeged/servo,fiji-flo/servo,mattnenterprise/servo,rnestler/servo,KiChjang/servo,SimonSapin/servo,nnethercote/servo,dsandeephegde/servo,notriddle/servo,paulrouget/servo,rnestler/servo,splav/servo,SimonSapin/servo,notriddle/servo,notriddle/servo