[dart:js_interop] Require top-level externals to have @JS

To refuse confusion between dart:ffi and dart:js_interop,
top-level externals will need to be annotated when using
dart:js_interop.

Change-Id: I1e4887eb32f135df94426e43fc885346f1b9f1b1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310485
Reviewed-by: Joshua Litt <joshualitt@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>

https://dart.googlesource.com/sdk/+/6fec16d48265493d06473c179b9662ea5eedeb6e
1 file changed
tree: bf7b3e2bd3b4d8eb2a7af4333ece3246cdb18786
  1. commits.json