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
/**
	 * Number of pixels to reserve for decorations.
	 */
	private static int RESERVED_WIDTH = 8;
	/**
	 * Cached platform flags for dealing with platform-specific issues.
	 */
	private static boolean CARBON = "carbon".equals(SWT.getPlatform()); 
	/**
	 * Constants describing the array indices used to hold the decorations in
	 * array slots.
	 */
	private static final int LEFT_TOP = 0;
	private static final int LEFT_BOTTOM = 1;
	private static final int RIGHT_TOP = 2;
	private static final int RIGHT_BOTTOM = 3;
	private static final int DECORATION_SLOTS = 4;
	/**
	 * Get the width (in pixels) that should always be reserved for field
	 * decorations, regardless of the actual width of any supplied decorations.