GitLab

- Computation of dropped frames now correctly accounts for multi-frame drops.
- A welcome side-effect is that variance of the percentage_dropped metric
  is reduced significantly.
- Heads-up for the perf sherrifs: percentage_dropped will increase quite a bit
  with this patch.

R=tonyg@chromium.org, nduca@chromium.org
BUG=264308

Review URL: https://chromiumcodereview.appspot.com/23998002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221825 0039d316-1c4b-4281-b951-d872f2087c98