Bug 124202 [Field Assist] - decorated fields should not size the created control
The philosophy of DecoratedField is that the client creates the target control and accesses it with normal SWT coding. The decorated field manages the decorations but otherwise statys out of the way. This philosophy is violated when DecoratedField sets the width of the field to IDialogConstants.ENTRY_WIDTH. Sizing decisions should be made by the client of the decorated field, not the field itself.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
* @param decoration
	 *            the decoration to be hidden.
	 */
	public void updateDecoration(FieldDecoration decoration) {
		FieldDecorationData data = getDecorationData(decoration);
		if (data == null)
			return;
		if (data.label != null) {
			data.label.setImage(decoration.getImage());
			
			
			if (data.label.getVisible() == true && hover != null) {
				showHoverText(decoration.getDescription(), data.label);
			}
		}
	}
	/*
	 * Set the visibility of the specified decoration data. This method does not
	 * change the visibility value stored in the decData, but instead consults
	 * it to determine how the visibility should be changed. This method is
	 * called any time visibility of a decoration might change, whether by
	 * client API or focus changes.
	 */
	private void setVisible(FieldDecorationData decData, boolean visible) {
		
		
		if (visible && decData.visible)
			decData.label.setVisible(true);
		else
			decData.label.setVisible(false);