Fix one more glitch when drag-attaching a tab to the tabstrip. Other tabs in...

Fix one more glitch when drag-attaching a tab to the tabstrip. Other tabs in the strip were instantly sized to their start size for the insert tab animation (which is their current size) but this calculation didn't take into account the fact that a newly inserted tab has a minimum size so their initial size isn't just the width / n other tabs, it's (width / n other tabs) - (min width / n other tabs)

B=1285677

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@90 0039d316-1c4b-4281-b951-d872f2087c98