Move echo_control.h to api/audio

Bug: webrtc:8844
Change-Id: I5c2406c43ade786c26e12b3c847fed8424283df0
Reviewed-on: https://webrtc-review.googlesource.com/53700
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22031}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index 4b74133..d55fd46 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -228,6 +228,15 @@
   deps = []
 }
 
+rtc_source_set("echo_control") {
+  visibility = [ "*" ]
+  sources = [
+    "audio/echo_control.h",
+  ]
+
+  deps = []
+}
+
 rtc_source_set("audio_options_api") {
   visibility = [ "*" ]
   sources = [