Bug 108493 [Markers] Show tooltips for table columns in marker views
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/provisional/views/markers/api/MarkerField.java
if (url == null)
			return null;
		return IDEWorkbenchPlugin.getDefault().getResourceManager()
				.createImageWithDefault(ImageDescriptor.createFromURL(url));
	}
	/**
	 * @return The text to be displayed in the column header for this field.
	 */
	public String getColumnHeaderText() {
		return configurationElement.getAttribute(MarkerSupportConstants.ATTRIBUTE_NAME);
	}
	/**
	 * Get the number of characters that should be reserved for the receiver.
	 * 
	 * @param control the control to scale from
	 * @return int
	 */
	public int getDefaultColumnWidth(Control control) {
		return 15 * getFontWidth(control);
	}
	/**
	 * Determine the average width of font used by the control.
	 * @param control
	 * @return int
	 */
	public final int getFontWidth(Control control) {
		GC gc = new GC(control.getDisplay());
		int width = gc.getFontMetrics().getAverageCharWidth();
		gc.dispose();
		return width;