[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/stats/BUILD.gn b/stats/BUILD.gn
index c67a5be..c16d8d1 100644
--- a/stats/BUILD.gn
+++ b/stats/BUILD.gn
@@ -25,6 +25,7 @@
 
   deps = [
     "../api:rtc_stats_api",
+    "../rtc_base:checks",
     "../rtc_base:rtc_base_approved",
   ]
 }
@@ -40,6 +41,7 @@
   deps = [
     ":rtc_stats",
     "../api:rtc_stats_api",
+    "../rtc_base:checks",
     "../rtc_base/system:rtc_export",
   ]
 }
@@ -61,6 +63,7 @@
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_base_tests_main",
       "../rtc_base:rtc_json",
+      "../test:test_support",
     ]
 
     if (is_android) {