Bug 125011 [Contributions] ActionContributionItem should use text for tooltip in toolitems
If an action is added to a toolbar, and it has a name, but no tooltip set, the name should be used as the tooltip (except when the text is actually displayed on the toolitem using setText()) Clients sometimes forget to set the tooltip text when no specific tooltip message exists.
bundles/org.eclipse.jface/src/org/eclipse/jface/action/ActionContributionItem.java
}
    /**
     * Shorten the given text <code>t</code> so that its length doesn't
     * exceed the given width. The default implementation replaces characters
     * in the center of the original string with an ellipsis ("..."). Override
     * if you need a different strategy.
     */
    protected String shortenText(String textValue, ToolItem item) {
        if (textValue == null)
            return null;
        GC gc = new GC(item.getParent());
        int maxWidth = item.getImage().getBounds().width * 4;
        if (gc.textExtent(textValue).x < maxWidth) {
            gc.dispose();
            return textValue;
        }
        for (int i = textValue.length(); i > 0; i--) {
            String test = textValue.substring(0, i);
            test = test + ellipsis;
            if (gc.textExtent(test).x < maxWidth) {
                gc.dispose();
                return test;
            }
        }
        gc.dispose();
        
        return textValue;
    }
}