[Cleanup] Add missing #include. Remove useless ones. IWYU part 2.

This is a follow-up to
https://webrtc-review.googlesource.com/c/src/+/106280.
This time the whole code base is covered.
Some files may have not been fixed though, whenever the IWYU tool
was breaking the build.

Bug: webrtc:8311
Change-Id: I2c31f552a87e887d33931d46e87b6208b1e483ef
Reviewed-on: https://webrtc-review.googlesource.com/c/111965
Commit-Queue: Yves Gerey <yvesg@google.com>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25830}
diff --git a/pc/rtcstats_integrationtest.cc b/pc/rtcstats_integrationtest.cc
index 49084de..0bf7660 100644
--- a/pc/rtcstats_integrationtest.cc
+++ b/pc/rtcstats_integrationtest.cc
@@ -8,16 +8,27 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <stdint.h>
+#include <string.h>
 #include <algorithm>
+#include <memory>
 #include <set>
+#include <string>
 #include <vector>
 
+#include "api/audio_codecs/audio_decoder_factory.h"
+#include "api/audio_codecs/audio_encoder_factory.h"
 #include "api/audio_codecs/builtin_audio_decoder_factory.h"
 #include "api/audio_codecs/builtin_audio_encoder_factory.h"
+#include "api/audio_options.h"
 #include "api/datachannelinterface.h"
 #include "api/peerconnectioninterface.h"
+#include "api/rtpreceiverinterface.h"
+#include "api/rtpsenderinterface.h"
+#include "api/stats/rtcstats.h"
 #include "api/stats/rtcstats_objects.h"
 #include "api/stats/rtcstatsreport.h"
+#include "api/test/fakeconstraints.h"
 #include "pc/rtcstatstraversal.h"
 #include "pc/test/peerconnectiontestwrapper.h"
 #include "pc/test/rtcstatsobtainer.h"
@@ -27,8 +38,10 @@
 #include "rtc_base/refcountedobject.h"
 #include "rtc_base/scoped_ref_ptr.h"
 #include "rtc_base/stringutils.h"
+#include "rtc_base/thread.h"
 #include "rtc_base/trace_event.h"
 #include "rtc_base/virtualsocketserver.h"
+#include "test/gtest.h"
 
 namespace webrtc {