Consider merging https://chromium.googlesource.com/chromium/blink/+/fc732005cac953cf3cc5229844d6755a1d39a052 There were many users of customStyleForRenderer() that were creating a custom style and then not marking it as unique. This normally wasn't an issue since the elements don't tend to be siblings of each other or at the same level of the tree, but could manifest in future form control types or the PasswordGeneratorButtonElement if we moved the calls to addToStyleSharingList (like future patches might). This patch adds all the missing setUnique() calls, but we should probably consider some more general solution in the future or get rid of the customStyleForRenderer() hook which is being used in bad ways all over the UA shadow elements.