Bug 287139 [CommonNavigator] Add core expression to determine initial activation for NCE
Build ID: 20090619-0625 Steps To Reproduce: Currently, the definition of the Navigator Content Extension via plugin.xml allows to specify the boolean attribute allowByDefault which controls if the contributed content is active by default. It makes sence to change the type of the attribute from boolean to core expression, which will allow to evaluate the default context and show content depending on it. This will ease the control of content and enhance the declarative configuration of CNF and NCEs. More information:
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptor.java
return icon;
	}
	/**
	 * @return Returns the suppressedExtensionId or null if none specified.
	 */
	public String getSuppressedExtensionId() {
		return suppressedExtensionId;
	}
	/**
	 * @return Returns the overridePolicy or null if this extension does not
	 *         override another extension.
	 */
	public OverridePolicy getOverridePolicy() {
		return overridePolicy;
	}
	/**
	 * @return Returns the contribution.
	 */
	public IPluginContribution getContribution() {
		return contribution;
	}
	/**
	 * The content provider could be an instance of
	 * {@link ICommonContentProvider}, but only {@link ITreeContentProvider} is
	 * required.
	 * 
	 * 
	 * @return An instance of the Content provider defined for this extension.
	 * @throws CoreException
	 *             if an instance of the executable extension could not be