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/ColorRegistry.java
}
    /**
     * Adds (or replaces) a color to this color registry under the given 
     * symbolic name.
     * <p>
     * A property change event is reported whenever the mapping from a symbolic
     * name to a color changes. The source of the event is this registry; the
     * property name is the symbolic color name.
     * </p>
     * 
     * @param symbolicName the symbolic color name
     * @param colorData an <code>RGB</code> object
     * @param update - fire a color mapping changed if true. False if this
     *            method is called from the get method as no setting has
     *            changed.
     */
    private void put(String symbolicName, RGB colorData, boolean update) {
        Assert.isNotNull(symbolicName);
        Assert.isNotNull(colorData);
        RGB existing = (RGB) stringToRGB.get(symbolicName);
        if (colorData.equals(existing))
            return;
        Color oldColor = (Color) stringToColor.remove(symbolicName);
        stringToRGB.put(symbolicName, colorData);
        if (update)
            fireMappingChanged(symbolicName, existing, colorData);
        if (oldColor != null)
            staleColors.add(oldColor);
    }
}