Makes Launcher remove itself as an observer from any windows it's observing in its destructor.
Makes Launcher remove itself as an observer from any windows it's
observing in its destructor.

BUG=none
TEST=none
R=ben@chromium.org

Review URL: http://codereview.chromium.org/8417002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@107612 0039d316-1c4b-4281-b951-d872f2087c98

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