Move rtc::FunctionView to the public API

Bug: webrtc:10138
Change-Id: Icc25a2a277a9608701aaddd546882366739991ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127898
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27227}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index f4e9f76..5882ade 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -79,6 +79,7 @@
     ":safe_minmax",
     ":type_traits",
     "../api:array_view",
+    "../api:function_view",
     "../api:scoped_refptr",
     "../system_wrappers:field_trial",
     "experiments:field_trial_parser",
@@ -1209,7 +1210,6 @@
       "critical_section_unittest.cc",
       "event_tracer_unittest.cc",
       "event_unittest.cc",
-      "function_view_unittest.cc",
       "logging_unittest.cc",
       "numerics/histogram_percentile_counter_unittest.cc",
       "numerics/mod_ops_unittest.cc",