Improving the form autofill menu behavior

This CL makes the form autofill popup menu behave like the Firefox's one, we only set the text field text when the user presses enter or click on an item.

It also prevents the WM_CHAR events to make it to the page after a WM_KEYDOWN has been processed by the menu (that would typically cause forms to proceed when you pressed enter in the form popup).

BUG=4145
TEST=Type something in a form to have the autofill popup showing. Use the down/up arrow to move around. The text should not change in the text field. Press enter, the selection should be set. Try again clicking this time.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=5149

[Matt Perry, 2008-11-06 02:14:27]

LGTM