NNTP: Limit the dragged item to the viewport boundaries.
NNTP: Limit the dragged item to the viewport boundaries.

BUG=16361, 15099

TEST=Drag the thumbnails on the new tab page and make sure that the
visual representation is never clipped. Also make sure that no new
scrollbars show up due to dragging.

Review URL: http://codereview.chromium.org/173090

git-svn-id: http://src.chromium.org/svn/trunk/src@23775 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: ac67f56030be61ef5958c07c27c3b54c5663c6ea
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser