Web Audio: Change the argument of AudioNode::addOutput().

This CL changes the argument of AudioNode::addOutput() from AudioNodeOutput* to
number-of-channels, and AudioNode::addOutput() creates AudioNodeOutput object.

This CL doesn't change user-visible behavior.

BUG=

Review URL: https://codereview.chromium.org/1023113002

git-svn-id: svn://svn.chromium.org/blink/trunk@192305 bbb929c8-8fbe-4397-9dbb-9b2b20218538
16 files changed