[Mac] Defer close from renderer while tab is a drag source.
[Mac] Defer close from renderer while tab is a drag source.

When dragging a link out of web content, pin the tab so that it
doesn't close out from under the drag.

BUG=26134
TEST=See bug for test.html.  View test.html.  Dragging link out should cause page to not close, and app should no longer crash.

Review URL: http://codereview.chromium.org/372023

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@31318 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