Remove locks from BufferQueue (not needed).

Also remove test code that can cause leaks into production.
Add sequence checkers.

Bug: webrtc:11988
Change-Id: I67b4cec6ee77d73ccffbbc88c9081ebb3c3cc423
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185503
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32228}
diff --git a/rtc_base/buffer_queue.h b/rtc_base/buffer_queue.h
index 29d1a5b..24a9b04 100644
--- a/rtc_base/buffer_queue.h
+++ b/rtc_base/buffer_queue.h
@@ -18,16 +18,16 @@
 
 #include "rtc_base/buffer.h"
 #include "rtc_base/constructor_magic.h"
-#include "rtc_base/synchronization/mutex.h"
+#include "rtc_base/synchronization/sequence_checker.h"
 #include "rtc_base/thread_annotations.h"
 
 namespace rtc {
 
-class BufferQueue {
+class BufferQueue final {
  public:
   // Creates a buffer queue with a given capacity and default buffer size.
   BufferQueue(size_t capacity, size_t default_size);
-  virtual ~BufferQueue();
+  ~BufferQueue();
 
   // Return number of queued buffers.
   size_t size() const;
@@ -44,17 +44,22 @@
   // Returns true unless no data could be written.
   bool WriteBack(const void* data, size_t bytes, size_t* bytes_written);
 
- protected:
-  // These methods are called when the state of the queue changes.
-  virtual void NotifyReadableForTest() {}
-  virtual void NotifyWritableForTest() {}
+  bool is_writable() const {
+    RTC_DCHECK_RUN_ON(&sequence_checker_);
+    return queue_.size() < capacity_;
+  }
+
+  bool is_readable() const {
+    RTC_DCHECK_RUN_ON(&sequence_checker_);
+    return !queue_.empty();
+  }
 
  private:
-  size_t capacity_;
-  size_t default_size_;
-  mutable webrtc::Mutex mutex_;
-  std::deque<Buffer*> queue_ RTC_GUARDED_BY(mutex_);
-  std::vector<Buffer*> free_list_ RTC_GUARDED_BY(mutex_);
+  webrtc::SequenceChecker sequence_checker_;
+  const size_t capacity_;
+  const size_t default_size_;
+  std::deque<Buffer*> queue_ RTC_GUARDED_BY(sequence_checker_);
+  std::vector<Buffer*> free_list_ RTC_GUARDED_BY(sequence_checker_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(BufferQueue);
 };