Update common_audio

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Moved src/ to webrtc/ to easily diff against the third_party/webrtc
   in the chromium tree

 * ARM/NEON/MIPS support is not yet hooked up

 * Tests have not been copied

webrtc/common_audio/signal_processing/downsample_fast.c

@@ -0,0 +1,48 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
+
+// TODO(Bjornv): Change the function parameter order to WebRTC code style.
+// C version of WebRtcSpl_DownsampleFast() for generic platforms.
+int WebRtcSpl_DownsampleFastC(const int16_t* data_in,
+                              size_t data_in_length,
+                              int16_t* data_out,
+                              size_t data_out_length,
+                              const int16_t* __restrict coefficients,
+                              size_t coefficients_length,
+                              int factor,
+                              size_t delay) {
+  size_t i = 0;
+  size_t j = 0;
+  int32_t out_s32 = 0;
+  size_t endpos = delay + factor * (data_out_length - 1) + 1;
+
+  // Return error if any of the running conditions doesn't meet.
+  if (data_out_length == 0 || coefficients_length == 0
+                           || data_in_length < endpos) {
+    return -1;
+  }
+
+  for (i = delay; i < endpos; i += factor) {
+    out_s32 = 2048;  // Round value, 0.5 in Q12.
+
+    for (j = 0; j < coefficients_length; j++) {
+      out_s32 += coefficients[j] * data_in[i - j];  // Q12.
+    }
+
+    out_s32 >>= 12;  // Q0.
+
+    // Saturate and store the output.
+    *data_out++ = WebRtcSpl_SatW32ToW16(out_s32);
+  }
+
+  return 0;
+}