WheelEvent's deltaX/deltaY sign is wrong

According to the specification, if a user agent scrolls as the default action
of the wheel event then the sign of the delta should be given by a right-hand
coordinate system where positive X, Y, and Z axes are directed towards the
right-most edge, bottom-most edge, and farthest depth (away from the user) of
the document, respectively:
http://www.w3.org/TR/DOM-Level-3-Events/#events-wheelevents

This signs for deltaX/deltaY are the inversed compared to the legacy
wheelDeltaX/wheelDeltaY. r156404 added support for DOM3 WheelEvent but used
the same sign for deltaX/deltaY and wheelDeltaX/wheelDeltaY.

Firefox 23 and IE10 uses the right sign according to the specification.

BUG=227454

Review URL: https://chromiumcodereview.appspot.com/22888005

git-svn-id: svn://svn.chromium.org/blink/trunk@156478 bbb929c8-8fbe-4397-9dbb-9b2b20218538