Since eglextchromium.h was replaced with eglext_angle.h in commit f5bb9dd7 this has caused an issue for external applications being updated to use it as it is missing a header dependency. The only response so far by angleproject on their bug was a non-committal unsupported. Have updated their bug to request equivalency of the old header.
https://bugs.chromium.org/p/angleproject/issues/detail?id=7617
Example case is for Kodi using CMake which fails its build test on this header due to missing defines (as it only tests on a single header at a time).