From 37a7db74e54625a0871cf45f889afb4eeee3e3a4 Mon Sep 17 00:00:00 2001
From: Paul Irish <paul.irish@gmail.com>
Date: Thu, 25 Oct 2018 14:23:15 -0700
Subject: [PATCH] core(driver): save performance.now() to avoid conflict
 (#6387)

---
 lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html | 5 ++++-
 lighthouse-core/gather/driver.js                         | 7 +++++--
 lighthouse-core/lib/page-functions.js                    | 8 ++++----
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html b/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
index 3e04e239da90..90b67ad93c54 100644
--- a/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
+++ b/lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
@@ -120,9 +120,12 @@
   Object.defineProperty(document.getElementById("5934b"), 'matches', {
     value: "blahblah"
   });
-  
   // Ensure gatherers still work when the prototype is messed with
   HTMLElement.prototype.matches = { value: "blahblah" };
+
+
+  // Ensure long-task collection still works when performance.now is redefined
+  window.performance.now = 'right now';
 </script>
 
 <div>
diff --git a/lighthouse-core/gather/driver.js b/lighthouse-core/gather/driver.js
index 771d80a20cad..8f278977eccf 100644
--- a/lighthouse-core/gather/driver.js
+++ b/lighthouse-core/gather/driver.js
@@ -1207,10 +1207,13 @@ class Driver {
    * @return {Promise<void>}
    */
   async cacheNatives() {
-    await this.evaluateScriptOnNewDocument(`window.__nativePromise = Promise;
+    await this.evaluateScriptOnNewDocument(`
+        window.__nativePromise = Promise;
         window.__nativeError = Error;
         window.__nativeURL = URL;
-        window.__ElementMatches = Element.prototype.matches;`);
+        window.__ElementMatches = Element.prototype.matches;
+        window.__perfNow = performance.now.bind(performance);
+    `);
   }
 
   /**
diff --git a/lighthouse-core/lib/page-functions.js b/lighthouse-core/lib/page-functions.js
index b759644e2e53..1b4ec164764e 100644
--- a/lighthouse-core/lib/page-functions.js
+++ b/lighthouse-core/lib/page-functions.js
@@ -37,7 +37,7 @@ function wrapRuntimeEvalErrorInBrowser(err) {
  */
 /* istanbul ignore next */
 function registerPerformanceObserverInPage() {
-  window.____lastLongTask = window.performance.now();
+  window.____lastLongTask = window.__perfNow();
   const observer = new window.PerformanceObserver(entryList => {
     const entries = entryList.getEntries();
     for (const entry of entries) {
@@ -64,12 +64,12 @@ function registerPerformanceObserverInPage() {
 function checkTimeSinceLastLongTask() {
   // Wait for a delta before returning so that we're sure the PerformanceObserver
   // has had time to register the last longtask
-  return new Promise(resolve => {
-    const timeoutRequested = window.performance.now() + 50;
+  return new window.__nativePromise(resolve => {
+    const timeoutRequested = window.__perfNow() + 50;
 
     setTimeout(() => {
       // Double check that a long task hasn't happened since setTimeout
-      const timeoutFired = window.performance.now();
+      const timeoutFired = window.__perfNow();
       const timeSinceLongTask = timeoutFired - timeoutRequested < 50 ?
           timeoutFired - window.____lastLongTask : 0;
       resolve(timeSinceLongTask);