Fix muted audio when playback rate != 1.0 or 0.0

      Rewrites the logic in AudioRendererAlgorithmBase to be able to output audio
at any point of a sped-up/slowed down window, instead of only outputting audio
in full multiples of windows.

BUG=108239
TEST=media_unittests, manual testing on video test matrix


Review URL: http://codereview.chromium.org/9395057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@125052 0039d316-1c4b-4281-b951-d872f2087c98