Source/Platform: Add audio hardware support for multi-channel by implementing AudioDestinationNode.maxChannelCount
https://bugs.webkit.org/show_bug.cgi?id=111385

Reviewed by James Robinson.

* chromium/public/Platform.h:
(WebKit::Platform::audioHardwareOutputChannels):

Source/WebCore: Add audio hardware support for multi-channel output by implementing AudioDestinationNode.maxChannelCount
https://bugs.webkit.org/show_bug.cgi?id=111385

Reviewed by James Robinson.

See specification details for .maxChannelCount:
https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#AudioDestinationNode

* Modules/webaudio/AudioDestinationNode.h:
(WebCore::AudioDestinationNode::maxChannelCount):
* Modules/webaudio/AudioDestinationNode.idl:
* Modules/webaudio/AudioNode.h:
Implement .maxChannelCount attribute.

(AudioNode):
* Modules/webaudio/DefaultAudioDestinationNode.h:
* Modules/webaudio/DefaultAudioDestinationNode.cpp:
(WebCore::DefaultAudioDestinationNode::initialize):
(WebCore::DefaultAudioDestinationNode::createDestination):
(WebCore::DefaultAudioDestinationNode::enableInput):
Call to createDestination() now takes no argument.
Instead we maintain a member variable for the input device ID.
(WebCore::DefaultAudioDestinationNode::maxChannelCount):
(WebCore::DefaultAudioDestinationNode::setChannelCount):
Check port-specific hardware support for maxChannelCount(),
and allow setting the channel count based on what the hardware
supports.

* platform/audio/AudioDestination.h:
(AudioDestination):
* platform/audio/chromium/AudioDestinationChromium.cpp:
(WebCore::AudioDestination::maxChannelCount):
(WebCore::AudioDestinationChromium::render):
Call into chromium WebKit API: audioHardwareOutputChannels().

* platform/audio/gstreamer/AudioDestinationGStreamer.cpp:
(WebCore::AudioDestination::maxChannelCount):
Add basic implementation for maxChannelCount() only supporting stereo output.

* platform/audio/mac/AudioDestinationMac.cpp:
(WebCore::AudioDestination::maxChannelCount):
Add basic implementation for maxChannelCount() only supporting stereo output.
Later, the mac port can support more than this with some small improvements to AudioDestinationMac.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144720 268f45cc-cd09-0410-ab3c-d52691b4dbfc