Added an "enable-audio-processor" flag and WebRtcAudioProcessor class.


This CL is a break-down CL from https://codereview.chromium.org/37793005. As the first step to move WebRtc APM to Chrome, it adds a enable-audio-processor command line flag, the WebRtcAudioProcessor class and its unittest.
WebRtcAudioProcessor is not hooked up the any of the code in Chrome yet, but it will be exercised and tested by its unittest.


TBR=tommi@chromium.org
BUG=264611
TEST=content_unittest

Review URL: https://codereview.chromium.org/88513002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237360 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237360