Revert "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)

Will reland in two different commits to preserve git blame history.

BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org

Change-Id: I550da8525aeb9c5b8f96338fcf1c9714f3dcdab1
Reviewed-on: https://chromium-review.googlesource.com/554610
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18820}

webrtc/base/win32socketinit.h

@@ -11,9 +11,10 @@
 #ifndef WEBRTC_BASE_WIN32SOCKETINIT_H_
 #define WEBRTC_BASE_WIN32SOCKETINIT_H_
 
+namespace rtc {
 
-// This header is deprecated and is just left here temporarily during
-// refactoring. See https://bugs.webrtc.org/7634 for more details.
-#include "webrtc/rtc_base/win32socketinit.h"
+void EnsureWinsockInit();
+
+}  // namespace rtc
 
 #endif  // WEBRTC_BASE_WIN32SOCKETINIT_H_