Bug 148357 [Field Assist] - API - provide access for closing the proposal popup
I think that the field assist API needs more hooks to be customizable. For example : 1) There is no way to manually close/open the popup. Most of the times, this is the easier thing for a user to ask to implement his custom behaviour. 2) There is no way to intercept keystrokes/events directed to the field. 3) There is no way to control focus.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
* setInitialPopupSize.
	 */
	private static final int POPUP_CHAR_HEIGHT = 10;
	/*
	 * The minimum pixel width for the popup. May be overridden by using
	 * setInitialPopupSize.
	 */
	private static final int POPUP_MINIMUM_WIDTH = 300;
	/*
	 * The pixel offset of the popup from the bottom corner of the control.
	 */
	private static final int POPUP_OFFSET = 3;
	/*
	 * Empty string.
	 */
	private static final String EMPTY = ""; 
	/*
	 * The object that provides content proposals.
	 */
	private IContentProposalProvider proposalProvider;
	/*
	 * A label provider used to display proposals in the popup, and to extract
	 * Strings from non-String proposals.
	 */
	private ILabelProvider labelProvider;
	/*
	 * The control for which content proposals are provided.
	 */
	private Control control;
	/*