The iterator used to walk through the set of throbbers might become invalid if a throbber decides it's done animating during the walk.  This might happen for toast throbbers, like the sad tab icon.
The iterator used to walk through the set of throbbers might become invalid
if a throbber decides it's done animating during the walk.  This might happen
for toast throbbers, like the sad tab icon.

TEST=none, really
BUG=20907
Review URL: http://codereview.chromium.org/185016

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@25316 0039d316-1c4b-4281-b951-d872f2087c98

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