Add some layout tests about behavior on undefined and null.

LayoutTests/fast/canvas/script-tests/canvas-currentTransform.js

 description("Series of tests to ensure correct behaviour of canvas.currentTransform");
 var ctx = document.createElement('canvas').getContext('2d');
 
 var matrix = ctx.currentTransform;
 
 debug("Check initial currentTransform values");
 shouldBe("matrix.a", "1");
 shouldBe("matrix.b", "0");
 shouldBe("matrix.c", "0");
 shouldBe("matrix.d", "1");
@@ skipping 157 matching lines @@
 ctx.fillRect(0, 0, 100, 100);
 
 imageData = ctx.getImageData(1, 1, 98, 98);
 imgdata = imageData.data;
 shouldBe("imgdata[4]", "0");
 shouldBe("imgdata[5]", "0");
 shouldBe("imgdata[6]", "255");
 
 debug("Check assigning an invalid object throws exception as expected");
 shouldThrow("ctx.currentTransform = ctx", '"TypeError: Failed to set the \'currentTransform\' property on \'CanvasRenderingContext2D\': The provided value is not of type \'SVGMatrix\'."');
+shouldThrow("ctx.currentTransform = undefined", '"TypeError: Failed to set the \'currentTransform\' property on \'CanvasRenderingContext2D\': The provided value is not of type \'SVGMatrix\'."');
+shouldThrow("ctx.currentTransform = null", '"TypeError: Failed to set the \'currentTransform\' property on \'CanvasRenderingContext2D\': The provided value is not of type \'SVGMatrix\'."');
 
 debug("Check handling non-finite values. see 2d.transformation.setTransform.nonfinite.html");
 ctx.fillStyle = 'red';
 ctx.fillRect(0, 0, 100, 100);
 
 function setCurrentTransformToNonfinite(ctx, a, b, c, d, e, f)
 {
     matrix.a = a;
     matrix.b = b;
     matrix.c = c;
@@ skipping 108 matching lines @@
 shouldBe("matrix.f", "10");
 
 ctx.fillStyle = 'green';
 ctx.fillRect(-100, -10, 100, 100);
 
 imageData = ctx.getImageData(1, 1, 98, 98);
 imgdata = imageData.data;
 shouldBe("imgdata[4]", "0");
 shouldBe("imgdata[5]", "128");
 shouldBe("imgdata[6]", "0");