Add missing #include to absl/memory/memory.h from audio_encoder_cng.cc

absl::make_unique is used in this file without absl/memory/memory.h
#include, that causes a build error on C++17 build of Chromium.

Bug: chromium:752720
Change-Id: I78fe9f76a6ea670a4250b4cf25c3c02cf4c4beb6
Reviewed-on: https://webrtc-review.googlesource.com/c/109540
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25514}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index f02a847..acd4996 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -189,6 +189,7 @@
     "../../api/audio_codecs:audio_codecs_api",
     "../../common_audio",
     "../../rtc_base:checks",
+    "//third_party/abseil-cpp/absl/memory",
   ]
 }