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/protobuf_utils.h b/webrtc/rtc_base/protobuf_utils.h
new file mode 100644
index 0000000..c8c98b0
--- /dev/null
+++ b/webrtc/rtc_base/protobuf_utils.h
@@ -0,0 +1,36 @@
+/*
+ *  Copyright (c) 2017 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.
+ */
+
+#include <string>
+
+#ifndef WEBRTC_RTC_BASE_PROTOBUF_UTILS_H_
+#define WEBRTC_RTC_BASE_PROTOBUF_UTILS_H_
+
+namespace webrtc {
+
+using ProtoString = std::string;
+
+}  // namespace webrtc
+
+#if WEBRTC_ENABLE_PROTOBUF
+
+#include "third_party/protobuf/src/google/protobuf/message_lite.h"
+#include "third_party/protobuf/src/google/protobuf/repeated_field.h"
+
+namespace webrtc {
+
+using google::protobuf::MessageLite;
+using google::protobuf::RepeatedPtrField;
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_ENABLE_PROTOBUF
+
+#endif  // WEBRTC_RTC_BASE_PROTOBUF_UTILS_H_