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

Reland the base->rtc_base without adding stub headers (will be
done in follow-up CL). This preserves git blame history of all files.

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

Change-Id: Iea3bb6f3f67b8374c96337b63e8f5aa3e6181012
Reviewed-on: https://chromium-review.googlesource.com/554611
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18821}
diff --git a/webrtc/rtc_base/compile_assert_c.h b/webrtc/rtc_base/compile_assert_c.h
new file mode 100644
index 0000000..591eda1
--- /dev/null
+++ b/webrtc/rtc_base/compile_assert_c.h
@@ -0,0 +1,21 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_RTC_BASE_COMPILE_ASSERT_C_H_
+#define 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_RTC_BASE_COMPILE_ASSERT_C_H_