Remove the last vestiges of audio_util.

- Removes GetHighLatencyOutputBufferSize() since we no longer
have any high latency users.  Fallback uses a minimum 2048
buffer size in AudioOutputResampler.
- Moves NumberOfWaveOutBuffers() to AudioManagerWin.  Documents
existing broken unit test edge case for Vista.
- Moves GetUserBufferSize() to AudioManagerBase as a protected
method.

BUG=120319
TEST=compiles

Review URL: https://codereview.chromium.org/25133002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226131 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226131