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

LayoutTests/fast/events/click-over-descendant-elements-expected.txt

 Check if any mousedown-mouseup pairs in one element dispatch click events.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 This test needs to run in a test environment.
 Very normal click on container:
 PASS lastClickTarget is container
 Move inside container:
 PASS lastClickTarget is container
 Move from container to a child:
 PASS lastClickTarget is container
 Move from a child to container:
 PASS lastClickTarget is container
 Move from a child to another child:
 PASS lastClickTarget is container
 Move out from a child:
 PASS lastClickTarget is document.body
 Removing a child element in the light DOM during a click:
 PASS lastClickTarget is null
 Click on escaping button content:
 PASS lastClickTarget is button1
 Click on disappearing INPUT value:
 PASS lastClickTarget is input1
+Mousedown on a form control, and mouseup on an element outside:
+PASS lastClickTarget is null
 PASS successfullyParsed is true
 
 TEST COMPLETE