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The CL also fixes the insertion position of the new item, so that the new item
is inserted behind of the existing selected item.  Previously the image item is
inserted ahead of the selected item. It changes the index of the selected item,
and it causes the inconsistency between the selected index and the selected
item.

BUG=392055
TEST=manually

Review URL: https://codereview.chromium.org/371333002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282044 0039d316-1c4b-4281-b951-d872f2087c98