Add stronger DCHECK for front and back timestamp calculations.

media/filters/audio_clock.cc

Index: media/filters/audio_clock.cc
diff --git a/media/filters/audio_clock.cc b/media/filters/audio_clock.cc
index 03af719bcb2348bb30c022f3de87d35f20483534..d4fea149e0c2b228a60252b5517aa93d0839c564 100644
--- a/media/filters/audio_clock.cc
+++ b/media/filters/audio_clock.cc
@@ -42,6 +42,7 @@ void AudioClock::WroteAudio(int frames_written,
   //
   // The ordering of compute -> push -> pop eliminates unnecessary memory
   // reallocations in cases where |buffered_| gets emptied.
+  const int64_t original_buffered_frames = total_buffered_frames_;

[jrummell, 2015/07/10 00:32:57]

Since this is only used in the DCHECK, will a release build complain about
unused variable?

[DaleCurtis, 2015/07/10 00:34:22]

Nope, the DCHECK still counts as usage.

   int64_t frames_played =
       std::max(INT64_C(0), total_buffered_frames_ - delay_frames);
   front_timestamp_ += ComputeBufferedMediaTime(frames_played);
@@ -52,6 +53,16 @@ void AudioClock::WroteAudio(int frames_written,
   back_timestamp_ += base::TimeDelta::FromMicroseconds(
       frames_written * playback_rate * microseconds_per_frame_);
 
+  // Ensure something crazy hasn't happened to desync the front and back values.
+  DCHECK_LE(front_timestamp_.InMicroseconds(), back_timestamp_.InMicroseconds())
+      << "frames_written=" << frames_written
+      << ", frames_requested=" << frames_requested
+      << ", delay_frames=" << delay_frames
+      << ", playback_rate=" << playback_rate
+      << ", frames_played=" << frames_played
+      << ", original_buffered_frames=" << original_buffered_frames
+      << ", total_buffered_frames_=" << total_buffered_frames_;
+
   // Update cached values.
   double scaled_frames = 0;
   double scaled_frames_at_same_rate = 0;