OfflineAudioContext should support up to 32 channels.

Source/modules/webaudio/OfflineAudioContext.cpp

 /*
  * Copyright (C) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 35 matching lines @@
         return nullptr;
     }
 
     Document* document = toDocument(context);
 
     if (!numberOfFrames) {
         exceptionState.throwDOMException(SyntaxError, "number of frames cannot be zero.");
         return nullptr;
     }
 
-    if (numberOfChannels > 10) {
-        exceptionState.throwDOMException(SyntaxError, "number of channels (" + String::number(numberOfChannels) + ") exceeds maximum (10).");
+    if (numberOfChannels > AudioContext::maxNumberOfChannels()) {
+        exceptionState.throwDOMException(
+            IndexSizeError,
+            ExceptionMessages::indexOutsideRange<unsigned>(
+                "number of channels",
+                numberOfChannels,
+                0,
+                ExceptionMessages::InclusiveBound,
+                AudioContext::maxNumberOfChannels(),
+                ExceptionMessages::InclusiveBound));
         return nullptr;
     }
 
     if (!isSampleRateRangeGood(sampleRate)) {
         exceptionState.throwDOMException(SyntaxError, "sample rate (" + String::number(sampleRate) + ") must be in the range 44100-96000 Hz.");
         return nullptr;
     }
 
     RefPtr<OfflineAudioContext> audioContext(adoptRef(new OfflineAudioContext(document, numberOfChannels, numberOfFrames, sampleRate)));
 
@@ skipping 16 matching lines @@
     ScriptWrappable::init(this);
 }
 
 OfflineAudioContext::~OfflineAudioContext()
 {
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)