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When BrowserActionOverflowMenuController is deleted, it deletes its associated
IconUpdaters. When these go away, they remove themselves as the observer on the
associated BrowserActionViews. This led to the use-after-free if the
BrowserActionOverflowMenuController outlasts any of the BrowserActionViews.

BUG=391061

Review URL: https://codereview.chromium.org/379483003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282224 0039d316-1c4b-4281-b951-d872f2087c98