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diff --git a/dom/canvas/test/webgl-conf/checkout/conformance/rendering/scissor-rect-repeated-rendering.html b/dom/canvas/test/webgl-conf/checkout/conformance/rendering/scissor-rect-repeated-rendering.html
new file mode 100644
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+++ b/dom/canvas/test/webgl-conf/checkout/conformance/rendering/scissor-rect-repeated-rendering.html
@@ -0,0 +1,63 @@
+<!--
+Copyright (c) 2019 The Khronos Group Inc.
+Use of this source code is governed by an MIT-style license that can be
+found in the LICENSE.txt file.
+-->
+
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Scissor Rectangle Repeated Rendering Test</title>
+<link rel="stylesheet" href="../../resources/js-test-style.css"/>
+<script src="../../js/js-test-pre.js"></script>
+<script src="../../js/webgl-test-utils.js"> </script>
+</head>
+<body>
+<canvas id="example" width="128" height="128"></canvas>
+<div id="description"></div>
+<div id="console"></div>
+<script>
+"use strict";
+
+description();
+debug('Regression test for <a href="https://code.google.com/p/chromium/issues/detail?id=778770">Chromium bug 778770</a>');
+
+var wtu = WebGLTestUtils;
+
+// These context creation attributes are significant to reproduce the bug.
+var gl = wtu.create3DContext("example", {alpha: false, antialias: false});
+
+// Draw into the upper right quadrant.
+var x      = 64;
+var y      = 64;
+var width  = 64;
+var height = 64;
+
+var numRenders = 10;
+
+function render() {
+    gl.viewport(x, y, width, height);
+    gl.scissor(x, y, width, height);
+    gl.enable(gl.SCISSOR_TEST);
+    gl.clearColor(0.0, 1.0, 0.0, 1.0);
+    gl.clear(gl.COLOR_BUFFER_BIT);
+
+    // If anything but black is ever seen in the un-drawn region of
+    // the canvas, the test fails.
+    var black = [0, 0, 0, 255];
+    wtu.checkCanvasRect(gl, 10, 10, 10, 10, black, "should be black", 1);
+
+    if (--numRenders > 0) {
+        window.requestAnimationFrame(render);
+    } else {
+        finishTest();
+    }
+}
+
+window.requestAnimationFrame(render);
+
+var successfullyParsed = true;
+</script>
+</body>
+</html>