Introduce AudioClock to improve playback delay calculations.

media/filters/audio_renderer_impl_unittest.cc

Index: media/filters/audio_renderer_impl_unittest.cc
diff --git a/media/filters/audio_renderer_impl_unittest.cc b/media/filters/audio_renderer_impl_unittest.cc
index 1ae27e35f48eb6b5b6d23fea5f2b65b53cdb1249..9190080b7d6872bb8375d55827eedb74195f9160 100644
--- a/media/filters/audio_renderer_impl_unittest.cc
+++ b/media/filters/audio_renderer_impl_unittest.cc
@@ -969,13 +969,14 @@ TEST_F(AudioRendererImplTest, TimeUpdatesOnFirstBuffer) {
   EXPECT_TRUE(ConsumeBufferedData(kFramesToConsume, NULL));
   WaitForPendingRead();
 
-  // Ensure we received a time update for the first buffer and it's zero.
+  // ConsumeBufferedData() uses an audio delay of zero, so ensure we received
+  // a time update that's equal to |kFramesToConsume| from above.
   timestamp_helper.SetBaseTimestamp(base::TimeDelta());
-  EXPECT_EQ(timestamp_helper.base_timestamp(), last_time_update());
   timestamp_helper.AddFrames(kFramesToConsume);
+  EXPECT_EQ(timestamp_helper.GetTimestamp(), last_time_update());
 
-  // ConsumeBufferedData() uses an audio delay of zero, so the next buffer
-  // should have a timestamp equal to the duration of |kFramesToConsume|.
+  // The next time update should match the remaining frames_buffered().
+  timestamp_helper.AddFrames(frames_buffered());
   EXPECT_TRUE(ConsumeBufferedData(frames_buffered(), NULL));
   EXPECT_EQ(timestamp_helper.GetTimestamp(), last_time_update());
 }