Delete class ChannelSendProxy

Replaced by interface ChannelSendInterface, implemented by ChannelSend
and mock class.

Thread checkers are moved to ChannelSend, which is also moved into
the anonymous namespace and exposed only via a function CreateChannelSend.

Bug: webrtc:9801
Change-Id: I73b2e2bfb67c1a5077709f2379533bf315babad9
Reviewed-on: https://webrtc-review.googlesource.com/c/111240
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25684}
diff --git a/audio/channel_receive.h b/audio/channel_receive.h
index fbfd7f0..ffdd196 100644
--- a/audio/channel_receive.h
+++ b/audio/channel_receive.h
@@ -62,7 +62,7 @@
 
 namespace voe {
 
-class ChannelSend;
+class ChannelSendInterface;
 
 // Interface class needed for AudioReceiveStream tests that use a
 // MockChannelReceive.
@@ -120,7 +120,8 @@
 
   // Associate to a send channel.
   // Used for obtaining RTT for a receive-only channel.
-  virtual void SetAssociatedSendChannel(const ChannelSend* channel) = 0;
+  virtual void SetAssociatedSendChannel(
+      const ChannelSendInterface* channel) = 0;
 
   virtual std::vector<RtpSource> GetSources() const = 0;
 };