Hotword: Fix always-on case by removing MS_CONFIGURED timeout

The behavior of MediaStreamAudioTrack::Configure() has changed:

Configure() used to be able to complete before any audio sample
is received because the AudioParameter can be obtained from a
WebRtcLocalAudioTrack according to
https://codereview.chromium.org/857093002

After the media stream refactoring http://crbug.com/577874
Configure() remains pending until the first audio frame is
received. For always-on hotword detection with a DSP audio
source, no audio sample is sent until the DSP detects a
potential hotword trigger.

This patch removes MS_CONFIGURED timeout so that the plugin
can keep waiting for a hotword instead of reporting a timeout
error.

BUG=616203
TEST=Verified always-on hotwording on Samus and Chell
Signed-off-by: Ben Zhang <benzh@chromium.org>
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2306803003
Cr-Commit-Position: refs/heads/master@{#418997}

chrome/browser/resources/hotword/nacl_manager.js

@@ -460,8 +460,12 @@ NaClManager.prototype.handleModelLoaded_ = function() {
     return;
   }
   this.sendDataToPlugin_(this.stream_.getAudioTracks()[0]);
-  this.waitForMessage_(hotword.constants.TimeoutMs.LONG,
-                       hotword.constants.NaClPlugin.MS_CONFIGURED);
+  // The plugin will send a MS_CONFIGURED, but don't set a timeout waiting for
+  // it. MediaStreamAudioTrack::Configure() will remain pending until the first
+  // audio buffer is received. When the audio source is a DSP for always-on
+  // detection, no audio sample is sent until the DSP detects a potential
+  // hotword trigger. Thus, Configure would remain pending indefinitely if we
+  // were to wait here. See https://crbug.com/616203
 };
 
 /**