Fix download shelf item overflow on os x.
Fix download shelf item overflow on os x.

This was regressed by the subview layout refactoring.

BUG=14672
TEST=download several items, resize window, make sure that no download item ever overlaps the "Show all downloads" link on the right.

Review URL: http://codereview.chromium.org/173048

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@24683 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