Consolidate the code path when window becomes invisible. This fixes a couple of focus related issues.
* focus didn't move when a window becomes invisible.
* transient parent didn't get focus if the transient child is removed from root hierarchy.

BUG=none
TEST=new test cases is added to root_window_event_filter.

Review URL: http://codereview.chromium.org/9398004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@122302 0039d316-1c4b-4281-b951-d872f2087c98

• ash/wm/root_window_event_filter_unittest.cc[diff]
• ash/wm/window_modality_controller.cc[diff]
• ash/wm/window_modality_controller_unittest.cc[diff]
• ui/aura/root_window.cc[diff]
• ui/aura/root_window.h[diff]