Fix custom buffer size support for WASAPI.

This allows any user buffer size which is an even divisor of
the endpoint buffer size.  I want this so I can play with
more buffer sizes on my home computer to try and address
glitching under load on Windows.

audio_parameters_are_valid_ wasn't really getting us anything
that we weren't already verifying during Open().

BUG=179058
TEST=compiles.

Review URL: https://codereview.chromium.org/117713004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242343 0039d316-1c4b-4281-b951-d872f2087c98
Telemetry: Add total-fast-path time to timeline metric.

Nice overview of all our high-priority threads.

TBR=ernstm@chromium.org
BUG=321439

Review URL: https://codereview.chromium.org/119723002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242344 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242344