Submitting user-submitted patch SDK-16863. You can change the tool tip class we create by setting ToolTipManager.toolTipClass. In ToolTipManagerImpl, we check if the created instance is a ToolTip to set its text. We should check if it's an IToolTip instead so we can support custom tooltip classes that implement IToolTip but don't necessarily extend ToolTip.
Bugs: SDK-13561, SDK-16863