Set channelCount and maxChannelCount correctly for OfflineAudioContext.

third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp

Index: third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp b/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
index 04edef246c88b263001690a05ddc2576e0642008..839218b2c46049990d422a47a21e8e7d27466a5a 100644
--- a/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp
@@ -49,6 +49,11 @@ OfflineAudioDestinationHandler::OfflineAudioDestinationHandler(AudioNode& node,
 {
     m_renderBus = AudioBus::create(renderTarget->numberOfChannels(), renderQuantumSize);
     m_framesToProcess = m_renderTarget->length();
+
+    // Node-specific defaults.
+    m_channelCount = m_renderTarget->numberOfChannels();
+    m_channelCountMode = Explicit;
+    m_channelInterpretation = AudioBus::Speakers;
 }
 
 PassRefPtr<OfflineAudioDestinationHandler> OfflineAudioDestinationHandler::create(AudioNode& node, AudioBuffer* renderTarget)
@@ -91,6 +96,11 @@ OfflineAudioContext* OfflineAudioDestinationHandler::context() const
     return static_cast<OfflineAudioContext*>(AudioDestinationHandler::context());
 }
 
+unsigned long OfflineAudioDestinationHandler::maxChannelCount() const
+{
+    return m_channelCount;
+}
+
 void OfflineAudioDestinationHandler::startRendering()
 {
     ASSERT(isMainThread());