Use testharness.js instead of js-test.js in LayoutTests/fast/canvas tests.

third_party/WebKit/LayoutTests/fast/canvas/canvas-pattern-modify.html

-<script src="../../resources/js-test.js"></script>
-<script src="canvas-pattern-modify.js"></script>
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script>
+// Based on http://philip.html5.org/tests/canvas/suite/tests/2d.pattern.modify.canvas1.html
+
+function pixelShouldBe(ctx, x, y, color) {
+    assert_array_equals(ctx.getImageData(x, y, 1, 1).data, color);
+}
+
+function createCanvasImage(width, height, color) {
+    var c = document.createElement("canvas");
+    c.width = width;
+    c.height = height;
+    var context = c.getContext("2d");
+    context.fillStyle = color;
+    context.fillRect(0, 0, width, height);
+    return c;
+}
+
+test(function(t) {
+    var canvas = createCanvasImage(100, 50, '#fff');
+    var ctx = canvas.getContext('2d');
+    
+    var patternCanvas = createCanvasImage(100, 50, '#0f0');
+    var pattern = ctx.createPattern(patternCanvas, 'no-repeat');
+    
+    // Modify the original canvas after we create a pattern.
+    var patternCtx = patternCanvas.getContext('2d');
+    patternCtx.fillStyle = '#f00';
+    patternCtx.fillRect(0, 0, 100, 50);
+    
+    ctx.fillStyle = pattern;
+    ctx.fillRect(0, 0, 100, 50);
+    
+    pixelShouldBe(ctx, 1, 1, [0, 255, 0, 255]);
+    pixelShouldBe(ctx, 98, 1, [0, 255, 0, 255]);
+    pixelShouldBe(ctx, 1, 48, [0, 255, 0, 255]);
+    pixelShouldBe(ctx, 98, 48, [0, 255, 0, 255]);
+}, "This test checks if pattern changes after the source canvas is modified. See https://bugs.webkit.org/show_bug.cgi?id=20578 .");
+</script>