diff --git a/lighthouse-core/lib/cdt/SDK.js b/lighthouse-core/lib/cdt/SDK.js
index 8615af63d0af..9c2232bbf1e9 100644
--- a/lighthouse-core/lib/cdt/SDK.js
+++ b/lighthouse-core/lib/cdt/SDK.js
@@ -14,44 +14,52 @@ const SDK = {
   ...require('./generated/sdk/SourceMap.js'),
 };
 
-// eslint-disable-next-line no-extend-native
-Object.defineProperty(Array.prototype, 'upperBound', {
-  /**
-   * Return index of the leftmost element that is greater
-   * than the specimen object. If there's no such element (i.e. all
-   * elements are smaller or equal to the specimen) returns right bound.
-   * The function works for sorted array.
-   * When specified, |left| (inclusive) and |right| (exclusive) indices
-   * define the search window.
-   *
-   * @param {!T} object
-   * @param {function(!T,!S):number=} comparator
-   * @param {number=} left
-   * @param {number=} right
-   * @return {number}
-   * @this {Array.<!S>}
-   * @template T,S
-   */
-  value: function(object, comparator, left, right) {
-    function defaultComparator(a, b) {
-      return a < b ? -1 : (a > b ? 1 : 0);
-    }
-    comparator = comparator || defaultComparator;
-    let l = left || 0;
-    let r = right !== undefined ? right : this.length;
-    while (l < r) {
-      const m = (l + r) >> 1;
-      if (comparator(object, this[m]) >= 0) {
-        l = m + 1;
-      } else {
-        r = m;
-      }
+const originalMappings = SDK.TextSourceMap.prototype.mappings;
+SDK.TextSourceMap.prototype.mappings = function() {
+  const mappings = originalMappings.call(this);
+  mappings.upperBound = upperBound.bind(mappings);
+  return mappings;
+};
+
+/**
+ * Return index of the leftmost element that is greater
+ * than the specimen object. If there's no such element (i.e. all
+ * elements are smaller or equal to the specimen) returns right bound.
+ * The function works for sorted array.
+ * When specified, |left| (inclusive) and |right| (exclusive) indices
+ * define the search window.
+ *
+ * @param {!T} object
+ * @param {function(!T,!S):number=} comparator
+ * @param {number=} left
+ * @param {number=} right
+ * @return {number}
+ * @this {Array.<!S>}
+ * @template T,S
+ */
+function upperBound(object, comparator, left, right) {
+  function defaultComparator(a, b) {
+    return a < b ? -1 : (a > b ? 1 : 0);
+  }
+  comparator = comparator || defaultComparator;
+  let l = left || 0;
+  let r = right !== undefined ? right : this.length;
+  while (l < r) {
+    const m = (l + r) >> 1;
+    if (comparator(object, this[m]) >= 0) {
+      l = m + 1;
+    } else {
+      r = m;
     }
-    return r;
-  },
-});
+  }
+  return r;
+};
 
-globalThis.cdt.SDK.TextSourceMap.prototype.findExactEntry = function(line, column) {
+/**
+ * @param {number} line
+ * @param {number} column
+ */
+SDK.TextSourceMap.prototype.findExactEntry = function(line, column) {
   // findEntry takes compiled locations and returns original locations.
   const entry = this.findEntry(line, column);
   // without an exact hit, we return no match
@@ -68,7 +76,7 @@ globalThis.cdt.SDK.TextSourceMap.prototype.findExactEntry = function(line, colum
 };
 
 // Add `lastColumnNumber` to mappings.
-globalThis.cdt.SDK.TextSourceMap.prototype.computeLastGeneratedColumns = function() {
+SDK.TextSourceMap.prototype.computeLastGeneratedColumns = function() {
   const mappings = this.mappings();
   if (mappings.length && typeof mappings[0].lastColumnNumber !== 'undefined') return;