Bug 118163 [Dialogs] - PopupDialog should define constants for zero margins
PopupDialogs traditionally use a 0 margin width and height for the grid layouts used. This should be made an API constant rather than subclasses just knowing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
Composite composite = new Composite(parent, SWT.NONE);
		GridLayout layout = new GridLayout();
		layout.marginHeight = POPUP_MARGINHEIGHT;
		layout.marginWidth = POPUP_MARGINWIDTH;
		layout.verticalSpacing = POPUP_VERTICALSPACING;
		composite.setLayout(layout);
		GridData gd = new GridData(GridData.FILL_BOTH);
		composite.setLayoutData(gd);
		return composite;
	}
	/**
	 * Returns the control that should get initial focus. Subclasses may
	 * override this method.
	 * 
	 * @return the Control that should receive focus when the popup opens.
	 */
	protected Control getFocusControl() {
		return dialogArea;
	}
	/**
	 * Sets the tab order for the popup. Clients should override to introduce
	 * specific tab ordering.
	 * 
	 * @param composite
	 *            the composite in which all content, including the title area
	 *            and info area, was created. This composite's parent is the
	 *            shell.
	 */
	protected void setTabOrder(Composite composite) {