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/helpers.h

@@ -0,0 +1,64 @@
+/*
+ *  Copyright 2004 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_HELPERS_H_
+#define WEBRTC_RTC_BASE_HELPERS_H_
+
+#include <string>
+#include "webrtc/base/basictypes.h"
+
+namespace rtc {
+
+// For testing, we can return predictable data.
+void SetRandomTestMode(bool test);
+
+// Initializes the RNG, and seeds it with the specified entropy.
+bool InitRandom(int seed);
+bool InitRandom(const char* seed, size_t len);
+
+// Generates a (cryptographically) random string of the given length.
+// We generate base64 values so that they will be printable.
+std::string CreateRandomString(size_t length);
+
+// Generates a (cryptographically) random string of the given length.
+// We generate base64 values so that they will be printable.
+// Return false if the random number generator failed.
+bool CreateRandomString(size_t length, std::string* str);
+
+// Generates a (cryptographically) random string of the given length,
+// with characters from the given table. Return false if the random
+// number generator failed.
+// For ease of implementation, the function requires that the table
+// size evenly divide 256; otherwise, it returns false.
+bool CreateRandomString(size_t length, const std::string& table,
+                        std::string* str);
+
+// Generates (cryptographically) random data of the given length.
+// Return false if the random number generator failed.
+bool CreateRandomData(size_t length, std::string* data);
+
+// Generates a (cryptographically) random UUID version 4 string.
+std::string CreateRandomUuid();
+
+// Generates a random id.
+uint32_t CreateRandomId();
+
+// Generates a 64 bit random id.
+uint64_t CreateRandomId64();
+
+// Generates a random id > 0.
+uint32_t CreateRandomNonZeroId();
+
+// Generates a random double between 0.0 (inclusive) and 1.0 (exclusive).
+double CreateRandomDouble();
+
+}  // namespace rtc
+
+#endif  // WEBRTC_RTC_BASE_HELPERS_H_