Add support for GCM cipher suites from RFC 7714.

webrtc/base/helpers.cc

 /*
  *  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.
  */
 
@@ skipping 227 matching lines @@
 bool CreateRandomString(size_t len, std::string* str) {
   return CreateRandomString(len, kBase64, 64, str);
 }
 
 bool CreateRandomString(size_t len, const std::string& table,
                         std::string* str) {
   return CreateRandomString(len, table.c_str(),
                             static_cast<int>(table.size()), str);
 }
 
+bool CreateRandomData(size_t length, std::string* data) {
+  data->resize(length);
+  // std::string is guaranteed to use contiguous memory in c++11 so we can
+  // safely write directly to it.
+  return Rng().Generate(&data->at(0), length);
+}
+
 // Version 4 UUID is of the form:
 // xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
 // Where 'x' is a hex digit, and 'y' is 8, 9, a or b.
 std::string CreateRandomUuid() {
   std::string str;
   std::unique_ptr<uint8_t[]> bytes(new uint8_t[31]);
   if (!Rng().Generate(bytes.get(), 31)) {
     LOG(LS_ERROR) << "Failed to generate random string!";
     return str;
   }
@@ skipping 41 matching lines @@
   } while (id == 0);
   return id;
 }
 
 double CreateRandomDouble() {
   return CreateRandomId() / (std::numeric_limits<uint32_t>::max() +
                              std::numeric_limits<double>::epsilon());
 }
 
 }  // namespace rtc