Prevent test shell editing events from getting to the webview delegate after test shell shutdown.
Prevent test shell editing events from getting to the webview delegate after test shell shutdown.

BUG=9486

Review URL: http://codereview.chromium.org/63091

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@13294 0039d316-1c4b-4281-b951-d872f2087c98

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