Don't paint the throbber animation while dragging.
Don't paint the throbber animation while dragging.

Windows doesn't paint the throbber either, so we match.  We can
probably add it back in if we want, but it might not be worth
the effort.

BUG=20750

Review URL: http://codereview.chromium.org/183039


git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@25128 0039d316-1c4b-4281-b951-d872f2087c98

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