9aa7c9a48 Export extern constants in embedder.h (flutter/engine#8550) (#30951)

https://github.com/flutter/engine/compare/f804c293f3ba...9aa7c9a48e93

git log f804c293f3baaec9ccec1e251293f6a3509223b8..9aa7c9a48e9342a450c3078e15c8d7923a338ede --no-merges --oneline
9aa7c9a48 Export extern constants in embedder.h (flutter/engine#8550)

The AutoRoll server is located here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff (jsimmons@google.com), and stop
the roller if necessary.