Assume pending buffered bytes is zero when ALSA has underrun.

media/audio/linux/alsa_output.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Creates an output stream based on the ALSA PCM interface.
 //
 // On device write failure, the stream will move itself to an invalid state.
 // No more data will be pulled from the data source, or written to the device.
 // All calls to public API functions will either no-op themselves, or return an
 // error if possible.  Specifically, If the stream is in an error state, Open()
@@ skipping 73 matching lines @@
   virtual void SetVolume(double volume);
   virtual void GetVolume(double* volume);
 
  private:
   friend class base::RefCountedThreadSafe<AlsaPcmOutputStream>;
   friend class AlsaPcmOutputStreamTest;
   FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_DeviceSelect);
   FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_FallbackDevices);
   FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_HintFail);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket);
+  FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_Negative);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_StopStream);
+  FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_Underrun);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_UnfinishedPacket);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ConstructedState);
   FRIEND_TEST(AlsaPcmOutputStreamTest, LatencyFloor);
   FRIEND_TEST(AlsaPcmOutputStreamTest, OpenClose);
   FRIEND_TEST(AlsaPcmOutputStreamTest, PcmOpenFailed);
   FRIEND_TEST(AlsaPcmOutputStreamTest, PcmSetParamsFailed);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ScheduleNextWrite);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ScheduleNextWrite_StopStream);
   FRIEND_TEST(AlsaPcmOutputStreamTest, StartStop);
   FRIEND_TEST(AlsaPcmOutputStreamTest, WritePacket_FinishedPacket);
@@ skipping 146 matching lines @@
   MessageLoop* client_thread_loop_;
 
   // The message loop responsible for querying the data source, and writing to
   // the output device.
   MessageLoop* message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(AlsaPcmOutputStream);
 };
 
 #endif  // MEDIA_AUDIO_LINUX_ALSA_OUTPUT_H_