Bug 147377 [Field Assist] - open proposal popup should close when there are no valid proposals left
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
/*
	 * Flag that indicates whether the adapter is enabled. In some cases,
	 * adapters may be installed but depend upon outside state.
	 */
	private boolean isEnabled = true;
	/*
	 * The delay in milliseconds used when autoactivating the popup.
	 */
	private int autoActivationDelay = 0;
	
	/*
	 * A boolean indicating whether a keystroke has been received.  
	 * Used to see if an autoactivation delay was interrupted by 
	 * a keystroke.
	 */
	private boolean receivedKeyDown;
	/*
	 * The desired size in pixels of the proposal popup.
	 */
	private Point popupSize;
	/*
	 * The remembered position of the insertion position. Not all controls will
	 * restore the insertion position if the proposal popup gets focus, so we
	 * need to remember it.
	 */
	private int insertionPos = -1;
	/**
	 * Construct a content proposal adapter that can assist the user with
	 * choosing content for the field.
	 *