Bug 65187 [Themes] Cascading*Registry leakage from Colors and Fonts pref page
Small leak on I20040529 For each ColorsAndFontsPreferencePage this is created, the cascading font and color registries are leaked. This is because the superclasses register a runnable with Display#disposeExec
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/FontRegistry.java
* @see org.eclipse.jface.resource.ResourceRegistry#getKeySet()
     */
    public Set getKeySet() {
        return Collections.unmodifiableSet(stringToFontData.keySet());
    }
    /* (non-Javadoc)
     * @see org.eclipse.jface.resource.ResourceRegistry#hasValueFor(java.lang.String)
     */
    public boolean hasValueFor(String fontKey) {
        return stringToFontData.containsKey(fontKey);
    }
    /* (non-Javadoc)
     * @see org.eclipse.jface.resource.ResourceRegistry#clearCaches()
     */
    protected void clearCaches() {
        Iterator iterator = stringToFontRecord.values().iterator();
        while (iterator.hasNext()) {
            Object next = iterator.next();
            ((FontRecord) next).dispose();
        }
        disposeFonts(staleFonts.iterator());
        stringToFontRecord.clear();
        staleFonts.clear();
    }
    /**
     * Dispose of all of the fonts in this iterator.
     * @param Iterator over Collection of Font
     */
    private void disposeFonts(Iterator iterator) {
        while (iterator.hasNext()) {