Add accounting of actual audio bit usage

Part of a set of CL to allow video to borrow underused audio bitrate.

Bug: webrtc:35055527
Change-Id: Idb504cbbc5794c06b28bdc21b3d860c9da9df175
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/358202
Reviewed-by: Jakob Ivarsson‎ <jakobi@webrtc.org>
Commit-Queue: Dan Tan <dwtan@google.com>
Cr-Commit-Position: refs/heads/main@{#42733}
diff --git a/audio/mock_voe_channel_proxy.h b/audio/mock_voe_channel_proxy.h
index 5836d88..607070a 100644
--- a/audio/mock_voe_channel_proxy.h
+++ b/audio/mock_voe_channel_proxy.h
@@ -182,6 +182,11 @@
       SetEncoderToPacketizerFrameTransformer,
       (rtc::scoped_refptr<webrtc::FrameTransformerInterface> frame_transformer),
       (override));
+  MOCK_METHOD(absl::optional<DataRate>, GetUsedRate, (), (const, override));
+  MOCK_METHOD(void,
+              RegisterPacketOverhead,
+              (int packet_byte_overhead),
+              (override));
 };
 }  // namespace test
 }  // namespace webrtc