https://bugs.webkit.org/show_bug.cgi?id=110172

Reviewed by Ryosuke Niwa.

Source/WebCore:

When a change in the focused node crosses a frame boundary, WebKit
doesn't always succeed in blurring the old focused node before focusing
the new one.

Each document remembers its focused node, and a Page-scoped
FocusController remembers the focused frame. If a new focused node is
in a different frame than the focused frame, FocusController tells the
old frame's document to clear its focused node before focusing the new
one (and remembering the new frame).

Unfortunately, web content can confuse FocusController by calling
window.focus() at the wrong time. Since window.focus() changes
FocusController's focused frame without focusing a new node,
FocusController won't think that a frame boundary is being crossed if a
node in this frame is later focused. Therefore it won't clear the old
frame's focused node (it won't even know which frame contained the old
focused node), causing at least two bugs:

1) The node in the old frame will not receive a blur event.
2) Calling document.activeElement on the main frame will return the
   previously focused node, but the HTML5 spec says it should return
   the frame owner element if a subframe has focus.

Fix both of these bugs by explicitly clearing the current frame's
focused node if window.focus() changes the focused frame. This fix
carries some compatibility risk by changing a long-standing behavior
of the engine (we've had this bug since the beginning of the project,
AFAICT). On the upside, it matches the behavior of both Firefox and IE,
matches what HTML5 says about subframe focus, and fixes at least one
well-known enterprise web app.

Tests: fast/dom/HTMLDocument/active-element-frames.html
       fast/frames/frame-focus-blurs-active-element.html

* page/DOMWindow.cpp:
(WebCore::DOMWindow::focus): If the frame being focused is not the same
as the currently focused frame, clear the currently focused frame's
focused node.

LayoutTests:

* fast/dom/HTMLDocument/active-element-frames-expected.txt:
* fast/dom/HTMLDocument/active-element-frames.html: Modified to run the
test a second time, focusing each element's frame before focusing the
element itself.
* fast/frames/frame-focus-blurs-active-element-expected.txt: Added.
* fast/frames/frame-focus-blurs-active-element.html: Added a test that
verifies a blur event is fired on the active element when a new frame
is focused.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143299 268f45cc-cd09-0410-ab3c-d52691b4dbfc