Move AudioRendererImpl construction to WebMediaPlayerImpl.

This is extracted from a larger CL created by scherkus@: https://codereview.chromium.org/11468033/

BUG=none
TEST=media_unittests pass


Review URL: https://chromiumcodereview.appspot.com/11564007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@173019 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed