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}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index acd54b9..0115429 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -615,6 +615,7 @@
 
 rtc_library("rtc_json") {
   public_configs = [ ":rtc_json_suppressions" ]
+  poisonous = [ "rtc_json" ]
   defines = []
   sources = [
     "strings/json.cc",