Fix refcounting error in file chooser.
Fix refcounting error in file chooser.

The proxy would release the resource before sending it but this reference is important because the Serialize function doesn't actually create another ref.

BUG=120669
TEST=


Review URL: http://codereview.chromium.org/9802032

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@129567 0039d316-1c4b-4281-b951-d872f2087c98

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