This reverts commit b2b7337ad4.
Reason for revert: flutter build broke!!
Original change's description:
> [dart:io] Stop forcing lower case on HttpHeaders
>
> This is a breaking change. Request: https://github.com/dart-lang/sdk/issues/33501
>
> HttpHeaders use lowercase by default for all headers, since it is supposed to be case insensitive. Some servers incorrectly treat case as significant, however, and expect headers with capitalization or in uppercase. The current implementation forces headers to be lower cases when adding values. Users cannot even manually modify the headers.
>
> This change removes this restriction here so that users can modify the headers to whatever form they want. The new behavior is backwards compatible except if class was implemented. All headers inside http.dart are written as lower cases, adding values to HttpHeaders is still receiving lower cases input.
>
> The other cl (https://dart-review.googlesource.com/c/http_multi_server/+/121411) migrates multi_headers.dart to be compatible with this change.
>
> Bug: https://github.com/dart-lang/sdk/issues/33501
> Change-Id: I6f7f2ef907b229773c283140c07f2de4cd500981
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/119100
> Commit-Queue: Zichang Guo <zichangguo@google.com>
> Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
TBR=whesse@google.com,sortie@google.com,lrn@google.com,zichangguo@google.com
Change-Id: I4d4299393ad6549b250053df8823e726855e2baf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: https://github.com/dart-lang/sdk/issues/33501
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134102
Reviewed-by: Zichang Guo <zichangguo@google.com>
Commit-Queue: Zichang Guo <zichangguo@google.com>
91a3ea89c8