Fix circular dependencies between optional, array_view, and rtc_base.

This splits things out of rtc_base and makes dependencies explicit.

Bug: webrtc:6828
Change-Id: Ib813c7bd9e4de7ab015acb917bc09ee7204ba7bd
Reviewed-on: https://webrtc-review.googlesource.com/31940
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21245}
diff --git a/rtc_base/pathutils.cc b/rtc_base/pathutils.cc
index 6ab8b24..b85d14f 100644
--- a/rtc_base/pathutils.cc
+++ b/rtc_base/pathutils.cc
@@ -9,7 +9,7 @@
  */
 
 #if defined(WEBRTC_WIN)
-#include "rtc_base/win32.h"
+#include <windows.h>
 #include <shellapi.h>
 #include <shlobj.h>
 #include <tchar.h>