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

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=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192305

[tkent, 2015-03-20 08:38:53]

tkent@chromium.org changed reviewers:
+ oilpan-reviews@chromium.org, rtoy@chromium.org

[tkent, 2015-03-20 08:38:54]

Please review this.

[haraken, 2015-03-20 13:48:10]

LGTM

[Raymond Toy, 2015-03-20 15:41:21]

lgtm

Is this a general cleanup or is it required for splitting each class into two?

[tkent, 2015-03-21 08:38:38]

> Is this a general cleanup or is it required for splitting each class into two?

Not mandatory, but these cleanups decrease the diff size of the main one.

[tkent, 2015-03-21 08:38:46]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2015-03-21 08:39:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1023113002/1

[commit-bot: I haz the power, 2015-03-21 13:32:28]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=192305