Add ToString() methods to classes with << operators, preparing for deprecations.

Bug: webrtc:8982
Change-Id: I9b8792a229539dd9848f4d9936fe343f4bf9ad49
Reviewed-on: https://webrtc-review.googlesource.com/63200
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22705}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 3c1b9f0..92088b0 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -334,6 +334,17 @@
   ]
 }
 
+rtc_source_set("audio_format_to_string") {
+  sources = [
+    "strings/audio_format_to_string.cc",
+    "strings/audio_format_to_string.h",
+  ]
+  deps = [
+    ":stringutils",
+    "../api/audio_codecs:audio_codecs_api",
+  ]
+}
+
 rtc_source_set("type_traits") {
   sources = [
     "type_traits.h",