Add multi channels support in AudioBus and AudioBufferSourceNode

Add multi channels support in AudioBus and AudioBufferSourceNode
https://bugs.webkit.org/show_bug.cgi?id=79017

Patch by Wei James <james.wei@intel.com> on 2012-02-22
Reviewed by Chris Rogers.

Source/WebCore:

Tests: webaudio/up-mixing-mono-51.html
       webaudio/up-mixing-mono-stereo.html
       webaudio/up-mixing-stereo-51.html

* platform/audio/AudioBus.cpp:
(WebCore::AudioBus::copyFrom):
(WebCore::AudioBus::sumFrom):
(WebCore::AudioBus::processWithGainFromMonoStereo):
(WebCore::AudioBus::processWithGainFrom):

LayoutTests:

* webaudio/resources/audio-testing.js:
(writeAudioBuffer):
* webaudio/resources/mix-testing.js: Added.
(createToneBuffer):
* webaudio/up-mixing-mono-51-expected.wav: Added.
* webaudio/up-mixing-mono-51.html: Added.
* webaudio/up-mixing-mono-stereo-expected.wav: Added.
* webaudio/up-mixing-mono-stereo.html: Added.
* webaudio/up-mixing-stereo-51-expected.wav: Added.
* webaudio/up-mixing-stereo-51.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108604 268f45cc-cd09-0410-ab3c-d52691b4dbfc