On some webpages (for example: stackoverflow.com), touch scrolling speed is too slow / fast when zoomed in / out.

The problem was that the zoom multiplier was applied twice:
- in handleGestureScrollUpdate
- somewhere deeper when handling wheel event

This patch fixes this issue, by passing unscaled value to EventHandler::sendScrollEventToView(...).

BUG=403304
TEST=Open stackoverflow.com, Set browser zoom to 50%, touch scroll  (sendScrollEventToView path)
TEST=Open http://goo.gl/OYhULR, Set browser zoom to 200%, touch scroll text area  (RenderBox path)

Review URL: https://codereview.chromium.org/472463002

git-svn-id: svn://svn.chromium.org/blink/trunk@183318 bbb929c8-8fbe-4397-9dbb-9b2b20218538