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}
diff --git a/webrtc/base/compile_assert_c.h b/webrtc/base/compile_assert_c.h
index 934cc9b..4d51de3 100644
--- a/webrtc/base/compile_assert_c.h
+++ b/webrtc/base/compile_assert_c.h
@@ -11,8 +11,11 @@
 #ifndef WEBRTC_BASE_COMPILE_ASSERT_C_H_
 #define WEBRTC_BASE_COMPILE_ASSERT_C_H_
 
-// 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/compile_assert_c.h"
+// Use this macro to verify at compile time that certain restrictions are met.
+// The argument is the boolean expression to evaluate.
+// Example:
+//   RTC_COMPILE_ASSERT(sizeof(foo) < 128);
+// Note: In C++, use static_assert instead!
+#define RTC_COMPILE_ASSERT(expression) switch (0) {case 0: case expression:;}
 
 #endif  // WEBRTC_BASE_COMPILE_ASSERT_C_H_