Do not handle mouse wheel events when Ctrl is pressed

This commit does not change existing behavior.

Previously, the renderer would not see Ctrl+scrollwheel at all, because
these were intercepted early and not passed to the renderer.
However, this has changed in https://codereview.chromium.org/165143003/,
to allow web pages to catch and handle the event.

To allow the browser to handle Ctrl+scrollwheel (zooming),
handleWheelEvent now ignores the event when Ctrl is pressed.

Contributed by Rob Wu <rob@robwu.nl>

BUG=111059

Review URL: https://codereview.chromium.org/168493002

git-svn-id: svn://svn.chromium.org/blink/trunk@167355 bbb929c8-8fbe-4397-9dbb-9b2b20218538