Introduce SignedExchangeParser interface

This CL intoduces SignedExchangeParser class and its public interface,
which implements streaming parser for signed exchange envelope format [1].

[1] https://wicg.github.io/webpackage/draft-yasskin-http-origin-signed-responses.html#rfc.section.5

Bug: 803774
Change-Id: I4f6eafd6cf873290656ea0f82edfc47864a677ec
Reviewed-on: https://chromium-review.googlesource.com/910528
Reviewed-by: Kunihiko Sakamoto <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Commit-Queue: Kouhei Ueno <[email protected]>
Cr-Commit-Position: refs/heads/master@{#535670}
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index dd72608d..0b59d84 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -1031,6 +1031,8 @@
     "loader/signed_exchange_header.h",
     "loader/signed_exchange_header_parser.cc",
     "loader/signed_exchange_header_parser.h",
+    "loader/signed_exchange_parser.cc",
+    "loader/signed_exchange_parser.h",
     "loader/signed_exchange_signature_verifier.cc",
     "loader/signed_exchange_signature_verifier.h",
     "loader/source_stream_to_data_pipe.cc",