Create an explicit lambda for onExit.
Create an explicit lambda for onExit.

This is needed because completer.complete() now takes an optional
argument. A function with an optional argument isn't a subtype of
the same function without the argument being optional.

Review URL: https://codereview.chromium.org//11794051

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@16817 260f80e4-7a28-3924-810f-c04153c831b5

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