gtk: Make sure we found the window corresponding to the XID of the window under the drag.
gtk: Make sure we found the window corresponding to the XID of the window under the drag.

BUG=19552
TEST=Drag a tab up and out of the tab strip.  This should not crash.
Review URL: http://codereview.chromium.org/174091

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@23768 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