Remove ourselves as a message loop observer in the tabstrip destructor to catch the case when the user closes the last tab in a tabstrip.  In this case, we add ourselves as a message loop observer and never get a chance to remove ourselves before the tabstrip is destroyed.
Remove ourselves as a message loop observer in the tabstrip destructor to catch the case when the user closes the last tab in a tabstrip.  In this case, we add ourselves as a message loop observer and never get a chance to remove ourselves before the tabstrip is destroyed.

BUG=14648
TEST=Open a new window and press the close button on the tab.  The browser should not crash.
Review URL: http://codereview.chromium.org/140006

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@18843 0039d316-1c4b-4281-b951-d872f2087c98

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