Introduce AudioOutputResampler for browser side resampling.

media/base/multi_channel_resampler_unittest.cc

Index: media/base/multi_channel_resampler_unittest.cc
diff --git a/media/base/multi_channel_resampler_unittest.cc b/media/base/multi_channel_resampler_unittest.cc
index d32396eb3e3a3173faab091871a92c6b63fb45a3..f046257046f946e822eefce151e411b96cad369e 100644
--- a/media/base/multi_channel_resampler_unittest.cc
+++ b/media/base/multi_channel_resampler_unittest.cc
@@ -63,6 +63,11 @@ class MultiChannelResamplerTest
             base::Unretained(this)));
     resampler.Resample(audio_bus_.get(), frames);
     TestValues(expected_max_rms_error, expected_max_error);
+
+    // Verify Flush() of our internal state.
+    EXPECT_NE(resampler.last_frame_count_, 0);
+    resampler.Flush();
+    EXPECT_EQ(resampler.last_frame_count_, 0);
   }
 
   void HighLatencyTest(int channels) {