The content attributes and presentational hints were implemented in
the #4289 pull request. This just implements the relevant IDL
attributes.
Source-Repo: https://github.com/servo/servo
Source-Revision: 500d5098655032465bdca5c6167f681078df0fc3
Extracted this out of #5649
This commit was created with the following commands:
```
find . -iname "*.webidl" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
```
find . -iname "*.rs" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
Source-Repo: https://github.com/servo/servo
Source-Revision: 4997d3a112354a407365fede1ab1944834a2e13c
