Return the IAccessible interface of the deepest descent that contains the speficied point in view accessibility's accHitTest. 
Return the IAccessible interface of the deepest descent that contains the speficied point in view accessibility's accHitTest. 

Previously accHitTest would
1. Only return a direct child that contained the specified point (accHitTest was called repeatedly until it returned CHILDID_SELF).
2. Always return a VT_I4 variant for a view that has no children instead of returing an IAccessible interface (which didn't work with the AT programs for some reason).

BUG=none
TEST=Manual: NVDA reads views on mouse overwith no children on mouse over like toolbar buttons.
TEST=Manual: AccExplorer32 and Inspect32 can select views with no children.

Review URL: http://codereview.chromium.org/3890003

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@63273 0039d316-1c4b-4281-b951-d872f2087c98

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