NNTP: Fix issue where dragged thumbnail had the wrong z-index.
NNTP: Fix issue where dragged thumbnail had the wrong z-index.

BUG=20903

TEST=Drag a thumbnail and release the mouse where you drqagged the
thumbnail from. Now, be quick, and drag the same thumbnail again. THe
thumbnail should not be displayed behind any other thumbnails.


Review URL: http://codereview.chromium.org/203006

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@25811 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser