Move ScrollTypes.h from Source/core/platform to Source/platform/scroll.

BUG=297477

Review URL: https://codereview.chromium.org/26306002

git-svn-id: svn://svn.chromium.org/blink/trunk@159056 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make fast/dom/timer-throttling-hidden-page.html less racy

Record previouseTime just before calling setTimeout, rather than much earlier.
Also use Date.now() instead of new Date().

R=ojan
BUG=234891

Review URL: https://codereview.chromium.org/26328003

git-svn-id: svn://svn.chromium.org/blink/trunk@159057 bbb929c8-8fbe-4397-9dbb-9b2b20218538