Use the lock when accessing the buffer object.

BUG=69195
TEST=play Z-Type for hours :)

Review URL: http://codereview.chromium.org/6157007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71211 0039d316-1c4b-4281-b951-d872f2087c98
static bool CheckParameters(AudioParameters params) {
  if (!params.IsValid())
    return false;
  return true;
}

static bool CheckParameters(AudioParameters params) {
  if (!params.IsValid())
    return false;
  return true;
}
