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

third_party/WebKit/LayoutTests/fast/canvas/canvas-blending-helpers.js

 var blendModes = ["source-over", "multiply", "screen", "overlay", "darken", "lighten", "color-dodge", "color-burn",
                   "hard-light", "soft-light", "difference", "exclusion", "hue", "saturation", "color", "luminosity"];
 
 // Helper functions for separate blend mode
 
 var separateBlendmodes = ["normal", "multiply", "screen", "overlay",
                           "darken", "lighten", "colorDodge","colorBurn",
                           "hardLight", "softLight", "difference", "exclusion"];
 
 var separateBlendFunctions = {
@@ skipping 282 matching lines @@
 function separateBlendColors(backdrop, source, blendModeIndex) {
     return applyBlendMode(backdrop, source, separateBlendFunctions[separateBlendmodes[blendModeIndex]]);
 }
 
 function nonSeparateBlendColors(backdrop, source, blendModeIndex) {
     var expectedColor = nonSeparateBlendFunctions[nonSeparateBlendModes[blendModeIndex]](backdrop, source);
     for (var i = 0; i < 3; ++i)
         expectedColor[i] = source[3] * (1 - backdrop[3]) * source[i] + source[3] * backdrop[3] * expectedColor[i] + (1 - source[3]) * backdrop[3] * backdrop[i];
     return [Math.round(255 * expectedColor[0]), Math.round(255 * expectedColor[1]), Math.round(255 * expectedColor[2]), 255];
 }
+
+function checkBlendModeResult(i, context, sigma) {
+    var actualColor = context.getImageData(0, 0, 1, 1).data;
+    var expectedColor = blendColors([129 / 255, 1, 129 / 255, 1], [1, 129 / 255, 129 / 255, 1], i);
+    assert_approx_equals(actualColor[0], expectedColor[0], sigma);
+    assert_approx_equals(actualColor[1], expectedColor[1], sigma);
+    assert_approx_equals(actualColor[2], expectedColor[2], sigma);
+    assert_approx_equals(actualColor[3], expectedColor[3], sigma);
+}