Added SwapChannels to AudioBus and swapped the channels when mirroring is enabled.


BUG=334273

Review URL: https://codereview.chromium.org/181493005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255036