Move proxies into pc/.

Bug: webrtc:12787
Change-Id: Ia244d9d22d35436a02cf5a448bd1520cb66ff352
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/220321
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34141}
diff --git a/pc/peer_connection_histogram_unittest.cc b/pc/peer_connection_histogram_unittest.cc
index 97fbde2..fa46ce9 100644
--- a/pc/peer_connection_histogram_unittest.cc
+++ b/pc/peer_connection_histogram_unittest.cc
@@ -19,7 +19,6 @@
 #include "api/jsep.h"
 #include "api/jsep_session_description.h"
 #include "api/peer_connection_interface.h"
-#include "api/peer_connection_proxy.h"
 #include "api/rtc_error.h"
 #include "api/scoped_refptr.h"
 #include "api/task_queue/default_task_queue_factory.h"
@@ -29,6 +28,7 @@
 #include "p2p/client/basic_port_allocator.h"
 #include "pc/peer_connection.h"
 #include "pc/peer_connection_factory.h"
+#include "pc/peer_connection_proxy.h"
 #include "pc/peer_connection_wrapper.h"
 #include "pc/sdp_utils.h"
 #include "pc/test/mock_peer_connection_observers.h"