Test that the viewer can handle the xlink:href attribute on linear gradients.

There are two rectangles. The top one has a simple blue (left) to red (right) linear gradient. The lower one has a different gradient definition, but should look the same as the one above, because the gradient makes a reference to the first gradient, without modifying any attribute.

The rendered picture should match the reference image, except for possible variations in the labelling text (per CSS2 rules).