Keep track of DTLS packet sizes to prevent partial reads.

The current use of rtc::FifoBuffer can lead to reading across DTLS packet
boundaries which could cause packets to not being processed correctly.

This CL introduces the new class rtc::BufferQueue and changes the
StreamInterfaceChannel to use it instead of the rtc::FifoBuffer.

BUG=chromium:447431
R=juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/52509004

Cr-Commit-Position: refs/heads/master@{#9254}

webrtc/base/bufferqueue.h

@@ -0,0 +1,50 @@
+/*
+ *  Copyright 2015 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_BASE_BUFFERQUEUE_H_
+#define WEBRTC_BASE_BUFFERQUEUE_H_
+
+#include <deque>
+#include <vector>
+
+#include "webrtc/base/buffer.h"
+#include "webrtc/base/criticalsection.h"
+
+namespace rtc {
+
+class BufferQueue {
+ public:
+  // Creates a buffer queue queue with a given capacity and default buffer size.
+  BufferQueue(size_t capacity, size_t default_size);
+  ~BufferQueue();
+
+  // Return number of queued buffers.
+  size_t size() const;
+
+  // ReadFront will only read one buffer at a time and will truncate buffers
+  // that don't fit in the passed memory.
+  bool ReadFront(void* data, size_t bytes, size_t* bytes_read);
+
+  // WriteBack always writes either the complete memory or nothing.
+  bool WriteBack(const void* data, size_t bytes, size_t* bytes_written);
+
+ private:
+  size_t capacity_;
+  size_t default_size_;
+  std::deque<Buffer*> queue_;
+  std::vector<Buffer*> free_list_;
+  mutable CriticalSection crit_;  // object lock
+
+  DISALLOW_COPY_AND_ASSIGN(BufferQueue);
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_BUFFERQUEUE_H_