Revert 239758 "Enable Audio/Video dev monitoring and Video captu..."

> Enable Audio/Video dev monitoring and Video capture via AVFoundation by default.
> 
> Flipping the command line flag from explicitly enabling AVFoundation to
> disable AVFoundation.
> 
> In the past there was a startup performance regression (http://crbug.com/311325 
> and http://crbug.com/311437), those type of regression should be monitored 
> carefully during the next couple of days.
> 
> BUG=288562
> 
> Review URL: https://codereview.chromium.org/101753003

TBR=mcasas@chromium.org

Review URL: https://codereview.chromium.org/112033003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239920 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239920