Adds support for 192kHz native output sample rate for WebRTC clients

Adds support for 192kHz native output sample rate for WebRTC clients

BUG=none
TEST=content_unittests and manual tests using different WebRTC clients in combination with 192kHz native sample rate on Win7

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=194911

[henrika (OOO until Aug 14), 2013-04-18 09:59:08]

xians@: please check this one. It seems like ~3% of our users would benefit by
this fix.

[no longer working on chromium, 2013-04-18 10:19:01]

On 2013/04/18 09:59:08, henrika wrote:
> xians@: please check this one. It seems like ~3% of our users would benefit by
> this fix.

lgtm

[commit-bot: I haz the power, 2013-04-18 10:58:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/henrika@chromium.org/14347002/1

[commit-bot: I haz the power, 2013-04-18 13:21:15]

Change committed as 194911

[DaleCurtis, 2013-04-18 17:19:39]

This may not work very well on OSX with the buffer sizes used by WebRTC and no
blocking shared memory.

[henrika (OOO until Aug 14), 2013-04-18 17:53:51]

I was not able to find an output device on Mac which supported 192 but it is not
clear how you can draw that conclusion at this stage. I will be glad to modify
if needed but would appreciate some more input on how you reason here. I could
use 96 for Mac and do 96->192 but that might not help. Or simply avoid
supporting 192 on Mac for now. What was the percentage of users on 192 on Mac?

[DaleCurtis, 2013-04-18 18:28:19]

The buffer size for 192kHz on OSX is 512 as of a couple weeks ago.  I assume
you're using 480 for 48kHz?

OSX @ 192kHz is 2% of our userbase:

https://uma.googleplex.com/histograms/?dayCount=1&version=All-M&group=Media&h...

[henrika (OOO until Aug 14), 2013-04-18 19:01:56]

480 is correct, i.e. FIFO from 480->512 in this case then.

[DaleCurtis, 2013-04-18 19:20:40]

The shared memory doesn't block on OSX though, so we likely end up with back to
back requests for 480 in the 192kHz case.

[henrika (OOO until Aug 14), 2013-04-18 19:44:43]

I will see if we can access a Mac which can use 192 to try it out.