Reland "Prefix flag macros with WEBRTC_."

This is a reland of 5ccdc1331fcc3cd78eaa14408fe0c38d37a5a51d

Original change's description:
> Prefix flag macros with WEBRTC_.
>
> Macros defined in rtc_base/flags.h are intended to be used to define
> flags in WebRTC's binaries (e.g. tests).
>
> They are currently not prefixed and this could cause problems with
> downstream clients since these names are quite common.
>
> This CL adds the 'WEBRTC_' prefix to them.
>
> Generated with:
>
> for x in DECLARE DEFINE; do
>   for y in bool int float string FLAG; do
>     git grep -l "\b$x\_$y\b" | \
>     xargs sed -i "s/\b$x\_$y\b/WEBRTC_$x\_$y/g"
>   done
> done
> git cl format
>
> Bug: webrtc:9884
> Change-Id: I7b524762b6a3e5aa5b2fc2395edd3e1a0fe72591
> Reviewed-on: https://webrtc-review.googlesource.com/c/106682
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25270}

TBR=kwiberg@webrtc.org

Bug: webrtc:9884
Change-Id: I5ba5368a231a334d135ed5e6fd7a279629ced8a3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/107161
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25277}
diff --git a/modules/audio_coding/neteq/tools/rtp_analyze.cc b/modules/audio_coding/neteq/tools/rtp_analyze.cc
index f939038..9d3041e 100644
--- a/modules/audio_coding/neteq/tools/rtp_analyze.cc
+++ b/modules/audio_coding/neteq/tools/rtp_analyze.cc
@@ -19,16 +19,16 @@
 #include "rtc_base/flags.h"
 
 // Define command line flags.
-DEFINE_int(red, 117, "RTP payload type for RED");
-DEFINE_int(audio_level,
-           -1,
-           "Extension ID for audio level (RFC 6464); "
-           "-1 not to print audio level");
-DEFINE_int(abs_send_time,
-           -1,
-           "Extension ID for absolute sender time; "
-           "-1 not to print absolute send time");
-DEFINE_bool(help, false, "Print this message");
+WEBRTC_DEFINE_int(red, 117, "RTP payload type for RED");
+WEBRTC_DEFINE_int(audio_level,
+                  -1,
+                  "Extension ID for audio level (RFC 6464); "
+                  "-1 not to print audio level");
+WEBRTC_DEFINE_int(abs_send_time,
+                  -1,
+                  "Extension ID for absolute sender time; "
+                  "-1 not to print absolute send time");
+WEBRTC_DEFINE_bool(help, false, "Print this message");
 
 int main(int argc, char* argv[]) {
   std::string program_name = argv[0];