GTK: Don't crash on end of download in newer GTKs.
GTK: Don't crash on end of download in newer GTKs.

BUG=102792
TEST=Doesn't crash after downloading a file in Ubuntu 11.10.


Review URL: http://codereview.chromium.org/8687020

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@112053 0039d316-1c4b-4281-b951-d872f2087c98

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