LibWeb/CSS: Fix reference bug when canonicalizing linear easing stops

+2 WPT tests

Tests/LibWeb/Text/input/wpt-import/css/css-easing/testcommon.js

@@ -0,0 +1,65 @@
+'use strict';
+
+// Creates a <div> element, appends it to the document body and
+// removes the created element during test cleanup.
+function createDiv(test, doc) {
+  return createElement(test, 'div', doc);
+}
+
+// Creates an element with the given |tagName|, appends it to the document body
+// and removes the created element during test cleanup.
+// If |tagName| is null or undefined, creates a <div> element.
+function createElement(test, tagName, doc) {
+  if (!doc) {
+    doc = document;
+  }
+  var element = doc.createElement(tagName || 'div');
+  doc.body.appendChild(element);
+  test.add_cleanup(function() {
+    element.remove();
+  });
+  return element;
+}
+
+// Convert px unit value to a Number
+function pxToNum(str) {
+  return Number(String(str).match(/^(-?[\d.]+)px$/)[1]);
+}
+
+// Cubic bezier with control points (0, 0), (x1, y1), (x2, y2), and (1, 1).
+function cubicBezier(x1, y1, x2, y2) {
+  function xForT(t) {
+    var omt = 1-t;
+    return 3 * omt * omt * t * x1 + 3 * omt * t * t * x2 + t * t * t;
+  }
+
+  function yForT(t) {
+    var omt = 1-t;
+    return 3 * omt * omt * t * y1 + 3 * omt * t * t * y2 + t * t * t;
+  }
+
+  function tForX(x) {
+    // Binary subdivision.
+    var mint = 0, maxt = 1;
+    for (var i = 0; i < 30; ++i) {
+      var guesst = (mint + maxt) / 2;
+      var guessx = xForT(guesst);
+      if (x < guessx) {
+        maxt = guesst;
+      } else {
+        mint = guesst;
+      }
+    }
+    return (mint + maxt) / 2;
+  }
+
+  return function bezierClosure(x) {
+    if (x == 0) {
+      return 0;
+    }
+    if (x == 1) {
+      return 1;
+    }
+    return yForT(tForX(x));
+  }
+}