getStaticResourceContent

	public String getResourceContent(StaticResource resource, String fileName) {
		String modStamp = String.valueOf(((DateTime)resource.SystemModStamp).getTime());

		List<String> path = new List<String>();
		path.add('/resource');
		path.add(modStamp);
		path.add(resource.Name);
		path.add(fileName);
		String url = String.join(path, '/');

		// PageReference .getContent() is not Testable.
		PageReference fileRef = new PageReference(url);
		return fileRef.getContent().toString();
	}