Add runtime enabled features API to webrtc.

API is not used anywhere for now. When depending projects implement it
or build with default implementation, it will be used.

Bug: webrtc:8287
Change-Id: I9e2aa922c2bb2b543793cd0561d797b02288ea6c
Reviewed-on: https://webrtc-review.googlesource.com/39042
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21611}

system_wrappers/BUILD.gn

@@ -52,6 +52,7 @@ rtc_static_library("system_wrappers") {
     ":cpu_features_api",
     ":field_trial_api",
     ":metrics_api",
+    ":runtime_enabled_features_api",
     "..:webrtc_common",
     "../:typedefs",
     "../api:optional",
@@ -127,6 +128,12 @@ rtc_source_set("field_trial_api") {
   ]
 }
 
+rtc_source_set("runtime_enabled_features_api") {
+  sources = [
+    "include/runtime_enabled_features.h",
+  ]
+}
+
 rtc_source_set("metrics_api") {
   visibility = [ "*" ]
   sources = [
@@ -150,6 +157,16 @@ rtc_source_set("field_trial_default") {
   ]
 }
 
+rtc_source_set("runtime_enabled_features_default") {
+  sources = [
+    "source/runtime_enabled_features_default.cc",
+  ]
+  deps = [
+    ":runtime_enabled_features_api",
+    "../rtc_base:rtc_base_approved",
+  ]
+}
+
 rtc_source_set("metrics_default") {
   visibility = [ "*" ]
   sources = [
@@ -166,6 +183,7 @@ group("system_wrappers_default") {
   deps = [
     ":field_trial_default",
     ":metrics_default",
+    ":runtime_enabled_features_default",
     ":system_wrappers",
   ]
 }

system_wrappers/include/field_trial.h

@@ -69,6 +69,12 @@ inline bool IsEnabled(const char* name) {
   return FindFullName(name).find("Enabled") == 0;
 }
 
+// Convenience method, returns true iff FindFullName(name) return a string that
+// starts with "Disabled".
+inline bool IsDisabled(const char* name) {
+  return FindFullName(name).find("Disabled") == 0;
+}
+
 }  // namespace field_trial
 }  // namespace webrtc
 

system_wrappers/include/runtime_enabled_features.h

@@ -0,0 +1,31 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef SYSTEM_WRAPPERS_INCLUDE_RUNTIME_ENABLED_FEATURES_H_
+#define SYSTEM_WRAPPERS_INCLUDE_RUNTIME_ENABLED_FEATURES_H_
+
+#include <string>
+
+// These functions for querying enabled runtime features must be implemented
+// by all webrtc clients (such as Chrome).
+// Default implementation is provided in:
+//
+//    system_wrappers/system_wrappers:runtime_enabled_features_default
+
+// TODO(ilnik): Find a more flexible way to use Chrome features.
+// This interface requires manual translation from feature name to
+// Chrome feature class in third_party/webrtc_overrides.
+namespace webrtc {
+namespace runtime_enabled_features {
+bool IsFeatureEnabled(std::string feature_name);
+
+}  // namespace runtime_enabled_features
+}  // namespace webrtc
+
+#endif  // SYSTEM_WRAPPERS_INCLUDE_RUNTIME_ENABLED_FEATURES_H_

system_wrappers/source/runtime_enabled_features_default.cc

@@ -0,0 +1,31 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "system_wrappers/include/runtime_enabled_features.h"
+
+#include "rtc_base/flags.h"
+
+namespace flags {
+DEFINE_bool(enable_dual_stream_mode,
+            false,
+            "Enables dual video stream mode.");
+}
+
+namespace webrtc {
+namespace runtime_enabled_features {
+
+bool IsFeatureEnabled(std::string feature_name) {
+  if (feature_name == "WebRtcDualStreamMode")
+    return flags::FLAG_enable_dual_stream_mode;
+  return false;
+}
+
+}  // namespace runtime_enabled_features
+}  // namespace webrtc