Relanding: Allow the DTLS fingerprint verification to occur after the handshake.

webrtc/base/buffer.h

 /*
  *  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 116 matching lines @@
   size_t size() const {
     RTC_DCHECK(IsConsistent());
     return size_;
   }
 
   size_t capacity() const {
     RTC_DCHECK(IsConsistent());
     return capacity_;
   }
 
+  bool empty() const { return size() == 0u; }
+
   BufferT& operator=(BufferT&& buf) {
     RTC_DCHECK(IsConsistent());
     RTC_DCHECK(buf.IsConsistent());
     size_ = buf.size_;
     capacity_ = buf.capacity_;
     data_ = std::move(buf.data_);
     buf.OnMovedFrom();
     return *this;
   }
 
@@ skipping 202 matching lines @@
   size_t capacity_;
   std::unique_ptr<T[]> data_;
 };
 
 // By far the most common sort of buffer.
 using Buffer = BufferT<uint8_t>;
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_BUFFER_H_