[Fuchsia] Change default AudioCapturer sampler rate to 16kHz

CastRunner redirects AudioCapturer to the parent agent. The
AudioCapturer implementation in the agent uses 16kHz sample rate
internally. Update default sample rate to 16kHz, so the agent
won't need to resample the stream.

Bug: 1059836
Change-Id: I7519485f8dfc7c56c527730cc3c90bbf689146c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2117161
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: David Dorwin <ddorwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752705}

media/audio/fuchsia/audio_manager_fuchsia.cc

@@ -48,10 +48,10 @@ AudioParameters AudioManagerFuchsia::GetInputStreamParameters(
   // TODO(crbug.com/852834): Fuchsia currently doesn't provide an API to get
   // device configuration. Update this method when that functionality is
   // implemented.
-  // Use 48kHz sample rate with 10ms buffer, which is consistent with
-  // the default configuration used on other platforms.
+  // Use 16kHz sample rate with 10ms buffer, which is consistent with
+  // the default configuration used in the AudioCapturer implementation.
   return AudioParameters(AudioParameters::AUDIO_PCM_LOW_LATENCY,
-                         CHANNEL_LAYOUT_MONO, 48000, 480);
+                         CHANNEL_LAYOUT_MONO, 16000, 160);
 }
 
 AudioParameters AudioManagerFuchsia::GetPreferredOutputStreamParameters(