We can get into a state where the automation framework presses the Close button in the Find box after the tab has been destroyed. This causes the Find box to act on a NULL web_contents_ pointer.
We now guard against this by checking for NULL web_contents before performing any work that relies on it.
(I can't reproduce this bug manually or by running the automation testing locally, but this is an attempt to fix the crash by using the information gathered from looking at the crash dump).
Review URL: http://codereview.chromium.org/27173
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@10414 0039d316-1c4b-4281-b951-d872f2087c98