Introduce AudioOutputResampler for browser side resampling.

media/base/multi_channel_resampler.cc

Index: media/base/multi_channel_resampler.cc
diff --git a/media/base/multi_channel_resampler.cc b/media/base/multi_channel_resampler.cc
index 960a212e9f8f6f617f0ea6b383da083bd977ec9d..b8df97d66c39d391e0e0187c7ac04d4da3e07501 100644
--- a/media/base/multi_channel_resampler.cc
+++ b/media/base/multi_channel_resampler.cc
@@ -94,4 +94,10 @@ void MultiChannelResampler::ProvideInput(int channel, float* destination,
   }
 }
 
+void MultiChannelResampler::Flush() {
+  last_frame_count_ = 0;
+  for (size_t i = 0; i < resamplers_.size(); ++i)
+    resamplers_[i]->Flush();
+}
+
 }  // namespace media