Note that I'm intentionally *not* leaving a blank line between the license
block and the "IWYU pragma" line, in nsDisplayItemTypesList.h. This matches the
prevailing style that I found in other files that have "IWYU pragma" lines.
I copied the boilerplate comment directly from the Coding Style MDN page:
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Coding_Style#Mode_Line
MozReview-Commit-ID: ACoHkDFe8Z3