net: Replace base::Optional and friends with absl counterparts

This replaces:
- base::Optional -> absl::optional
- include "base/optional.h"
  ->
  include "third_party/abseil-cpp/absl/types/optional.h"
- base::nullopt -> absl::nullopt
- base::make_optional -> absl::make_optional

Bug: 1202909
Change-Id: I27d6f81f415e213c1a4997a55c35935a57ba88a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2896994
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Owners-Override: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#883294}
NOKEYCHECK=True
GitOrigin-RevId: 068d29106afcc2435307d2d2067a014a018d8ec7
diff --git a/run_testserver.cc b/run_testserver.cc
index 04a7c4a..f3a8bce 100644
--- a/run_testserver.cc
+++ b/run_testserver.cc
@@ -51,7 +51,7 @@
   }
 
   // If populated, EmbeddedTestServer is used instead of the SpawnedTestServer.
-  base::Optional<net::test_server::EmbeddedTestServer::Type>
+  absl::optional<net::test_server::EmbeddedTestServer::Type>
       embedded_test_server_type;
 
   net::SpawnedTestServer::Type server_type;