Don't dispatch a 'click' event for mousedown/mouseup across form controls.

This CL fixes a regression by r162081 [1].

The behavior change by r162081 was correct according to the standard, however it
caused unexpected behavior on some sites.  IE11 doesn't dispatch a click event
if a mousedown event happened on a form control, and a mouseup event happened on
anoter element. We follow it.

[1] http://src.chromium.org/viewvc/blink?revision=162081&view=revision

BUG=328304, 329136
TEST=automated

Review URL: https://codereview.chromium.org/110173005

git-svn-id: svn://svn.chromium.org/blink/trunk@164073 bbb929c8-8fbe-4397-9dbb-9b2b20218538