This is due to a missing call to DataGrid.updateWidths() -- one liner fix.
Created attachment 91083 [details] patch
Manually committed http://trac.webkit.org/changeset/84898 2011-04-26 Mikhail Naganov <mnaganov@chromium.org> Reviewed by Pavel Feldman. Web Inspector: [Chromium] Fix columns resizing in the detailed heap snapshot grids. https://bugs.webkit.org/show_bug.cgi?id=59438 * inspector/front-end/DetailedHeapshotView.js: (WebInspector.DetailedHeapshotView.prototype._changeView):