Remove runtime_enabled_features from WebRTC.

While working on removing field_trial_default and metrics_default
(in order to avoid link time replacement and use better defaults), we
discovered that runtime_enabled_features (which also has a _default
implementation) is not used (more info on this here:
https://bugs.chromium.org/p/webrtc/issues/detail?id=9631#c21).

Usage of this code has been removed in WebRTC with this CL:
https://webrtc-review.googlesource.com/c/src/+/102361.

Bug: webrtc:9631
Change-Id: Ief33059cd329f429b9bbdd7520808e62e3f6f62b
Reviewed-on: https://chromium-review.googlesource.com/1249029Reviewed-by: Henrik Grunell <grunell@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595040}

third_party/webrtc_overrides/BUILD.gn

@@ -39,7 +39,7 @@ group("jingle_deps") {
   ]
 }
 
-static_library("webrtc") {
+source_set("webrtc") {
   public_deps = [
     ":jingle_deps",
 
@@ -57,29 +57,22 @@ static_library("webrtc") {
     cflags = [ "/wd4005" ]
   }
 
-  # When WebRTC is built as part of Chromium it should exclude the default
-  # implementation of field_trial unless it is building for NACL or Chromecast.
+  # When Chromium is built for NACL or Chromecast, WebRTC provides a
+  # field_trial implementation so there is no need to depend on
+  # ":field_trial".
   # This configuration happens here:
   # https://cs.chromium.org/chromium/src/third_party/webrtc/webrtc.gni?l=44-51&rcl=95c56eebe0a2b31ad5752138d15b431124e17d36
   if (is_nacl) {
     deps += [
       "//native_client_sdk/src/libraries/nacl_io",
-      "//third_party/webrtc/system_wrappers:runtime_enabled_features_default",
-    ]
-  } else if (is_chromecast) {
-    deps += [
-      "//third_party/webrtc/system_wrappers:runtime_enabled_features_default",
-    ]
-  } else {
-    # Otherwise, we just add the field_trial which redirects to base and
-    # runtime_enabled_features which redirects to content/public/common.
-    sources = [
-      "runtime_enabled_features.cc",
     ]
+  } else if (!is_chromecast) {
+    # When Chromium doesn't build for NaCL or Chromecast, WebRTC doesn't
+    # provide an implementation for field_trial and a custom one (that uses
+    # base/metrics/field_trial.h is provided).
     deps += [
       ":field_trial",
       "//base",
-      "//third_party/webrtc/system_wrappers:runtime_enabled_features_api",
     ]
   }
 

third_party/webrtc_overrides/runtime_enabled_features.cc

-// Copyright 2018 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-//
-// Define webrtc::runtime_features::IsFeatureEnabled to provide webrtc with a
-// chromium runtime flags access.
-
-#include "base/feature_list.h"
-#include "third_party/webrtc/system_wrappers/include/runtime_enabled_features.h"
-
-namespace webrtc {
-
-namespace runtime_enabled_features {
-
-const base::Feature kWebRtcDualStreamMode{"WebRTC-DualStreamMode",
-                                          base::FEATURE_DISABLED_BY_DEFAULT};
-
-bool IsFeatureEnabled(std::string feature_name) {
-  if (feature_name == kDualStreamModeFeatureName)
-    return base::FeatureList::IsEnabled(kWebRtcDualStreamMode);
-  return false;
-}
-
-}  // namespace runtime_enabled_features
-
-}  // namespace webrtc