Revert 162362 "File constructor understands lastModified."

Likely causing fast/files/file-constructor.html to be flaky on windows
(reliably faling on XP)

See http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&showExpectations=true&tests=fast%2Ffiles%2Ffile-constructor.html

> File constructor understands lastModified.
> 
> BUG=164933
> 
> Review URL: https://codereview.chromium.org/74213009

TBR=costan@gmail.com

Review URL: https://codereview.chromium.org/79343006

git-svn-id: svn://svn.chromium.org/blink/trunk@162424 bbb929c8-8fbe-4397-9dbb-9b2b20218538