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}

webrtc/rtc_base/optionsfile.h

@@ -0,0 +1,50 @@
+/*
+ *  Copyright 2008 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_OPTIONSFILE_H_
+#define WEBRTC_RTC_BASE_OPTIONSFILE_H_
+
+#include <map>
+#include <string>
+
+namespace rtc {
+
+// Implements storage of simple options in a text file on disk. This is
+// cross-platform, but it is intended mostly for Linux where there is no
+// first-class options storage system.
+class OptionsFile {
+ public:
+  OptionsFile(const std::string &path);
+  ~OptionsFile();
+
+  // Loads the file from disk, overwriting the in-memory values.
+  bool Load();
+  // Saves the contents in memory, overwriting the on-disk values.
+  bool Save();
+
+  bool GetStringValue(const std::string& option, std::string* out_val) const;
+  bool GetIntValue(const std::string& option, int* out_val) const;
+  bool SetStringValue(const std::string& option, const std::string& val);
+  bool SetIntValue(const std::string& option, int val);
+  bool RemoveValue(const std::string& option);
+
+ private:
+  typedef std::map<std::string, std::string> OptionsMap;
+
+  static bool IsLegalName(const std::string &name);
+  static bool IsLegalValue(const std::string &value);
+
+  std::string path_;
+  OptionsMap options_;
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_RTC_BASE_OPTIONSFILE_H_