Make rtc_json poisonous in WebRTC

This does not help the attached bugs, but it does allow greater control
over what JSON code is running where. Long-term, the JSON library used
for parsing configuration should likely be a library already present
in Chromium builds, to avoid duplication. And if that happens, then
WebRTC bug 9804 may be passé.

Note that this CL also sorts our poisons alphabetically.

Bug: chromium:895814, webrtc:9804
Change-Id: I70c3efe05a0eba9212895407f73978d8216df920
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158400
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29615}

BUILD.gn

@@ -711,8 +711,11 @@ if (rtc_include_tests) {
 group("poison_audio_codecs") {
 }
 
-group("poison_software_video_codecs") {
-}
-
 group("poison_default_task_queue") {
 }
+
+group("poison_rtc_json") {
+}
+
+group("poison_software_video_codecs") {
+}

api/audio/BUILD.gn

@@ -52,6 +52,7 @@ rtc_library("aec3_config") {
 
 rtc_library("aec3_config_json") {
   visibility = [ "*" ]
+  allow_poison = [ "rtc_json" ]
   sources = [
     "echo_canceller3_config_json.cc",
     "echo_canceller3_config_json.h",

rtc_base/BUILD.gn

@@ -615,6 +615,7 @@ config("rtc_json_suppressions") {
 
 rtc_library("rtc_json") {
   public_configs = [ ":rtc_json_suppressions" ]
+  poisonous = [ "rtc_json" ]
   defines = []
   sources = [
     "strings/json.cc",

webrtc.gni

@@ -366,11 +366,14 @@ all_poison_types = [
   # Encoders and decoders for specific audio codecs such as Opus and iSAC.
   "audio_codecs",
 
-  # Software video codecs (VP8 and VP9 through libvpx).
-  "software_video_codecs",
-
   # Default task queue implementation.
   "default_task_queue",
+
+  # JSON parsing should not be needed in the "slim and modular" WebRTC.
+  "rtc_json",
+
+  # Software video codecs (VP8 and VP9 through libvpx).
+  "software_video_codecs",
 ]
 
 absl_include_config = "//third_party/abseil-cpp:absl_include_config"