Auto merge of #26166 - utsavoza:ugo/issue-23436/08-04-2020, r=jdm

Remove DomRefCell wrapper for CanvasState

<!-- 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
- [x] These changes fix #23436
- [x] There are tests for these changes

The PR removes the DomRefCell wrapper for CanvasState from `CanvasRenderingContext2D` and `OffscreenCanvasRenderingContext2D`. The reason for keeping member wrappers in CanvasState instead of overall CanvasState wrapper itself is because I believe that removing member wrappers would make it rather difficult to refactor the internal CanvasState methods in order to cover certain edge cases.

[For example](https://github.com/servo/servo/issues/23436#issuecomment-611089157): Drawing a canvas inside of itself would require getting and providing certain parameters for source canvas such as `canvas_id` and `is_origin_clean` that are currently accessed through source canvas context. Also, we might run into similar issue when creating patterns using canvas.

<!-- 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. -->

0 files changed, 0 insertions, 0 deletions