Fix DnD jank
Fix DnD jank

The mouseover code I added to do *smart* tooltips was making DnD almost
unusable.

BUG=None

TEST=Drag thumbnails on the NNTP and they should move smoothly.

Review URL: http://codereview.chromium.org/149427

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@20413 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