Add GetStats to MockAudioDevice.

Bug: b/496439120
Change-Id: I58337260f8aa1c619ba666fc6317f1b5dd6c1d51
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/473600
Commit-Queue: Viktor Grönroos <wilhelmsson@google.com>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47730}

modules/audio_device/include/mock_audio_device.h

diff --git a/modules/audio_device/include/mock_audio_device.h b/modules/audio_device/include/mock_audio_device.h
index 276a0b5..850d73d 100644
--- a/modules/audio_device/include/mock_audio_device.h
+++ b/modules/audio_device/include/mock_audio_device.h
@@ -12,6 +12,7 @@
 #define MODULES_AUDIO_DEVICE_INCLUDE_MOCK_AUDIO_DEVICE_H_
 
 #include <cstdint>
+#include <optional>
 
 #include "api/audio/audio_device.h"
 #include "api/audio/audio_device_defines.h"
@@ -140,6 +141,7 @@
   MOCK_METHOD(int32_t, EnableBuiltInAGC, (bool enable), (override));
   MOCK_METHOD(int32_t, EnableBuiltInNS, (bool enable), (override));
   MOCK_METHOD(int32_t, GetPlayoutUnderrunCount, (), (const, override));
+  MOCK_METHOD(std::optional<Stats>, GetStats, (), (const, override));
 #if defined(WEBRTC_IOS)
   MOCK_METHOD(int,
               GetPlayoutAudioParameters,