Use monotonic finish time for sync request completion.

Currently wall time is used. That is wrong.

Since request is performed synchronously, current time fits well as
finish time.

BUG=309570

Review URL: https://codereview.chromium.org/47603003

git-svn-id: svn://svn.chromium.org/blink/trunk@160817 bbb929c8-8fbe-4397-9dbb-9b2b20218538