GTK: fix site type icon dragging.
GTK: fix site type icon dragging.

Don't connect to the drag events more than once.

BUG=45270
TEST=dragging that box in debug mode, no backtrace

Review URL: http://codereview.chromium.org/2514001

git-svn-id: http://src.chromium.org/svn/trunk/src@48780 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 865ac456645d8586af8e3e05198fba53aa923f79
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