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
e.y += hm * 2;
			return e;
		}
		/*
		 * Compute a new shape for the hover shell.
		 */
		void setNewShape() {
			Region oldRegion = region;
			region = new Region();
			region.add(getPolygon(false));
			hoverShell.setRegion(region);
			if (oldRegion != null) {
				oldRegion.dispose();
			}
		}
	}
	/**
	 * Construct a decorated field which is parented by the specified composite
	 * and has the given style bits. Use the controlCreator to create the
	 * specific kind of control that is decorated inside the field.
	 * 
	 * @param parent
	 *            the parent of the decorated field.
	 * @param style
	 *            the desired style bits for the field.
	 * @param controlCreator
	 *            the IControlCreator used to specify the specific kind of
	 *            control that is to be decorated.
	 * 
	 * @see IControlCreator