From a3bdc3242ffc675db5320eb1e3ca5bd92d020158 Mon Sep 17 00:00:00 2001
From: Rick Byers <rbyers@chromium.org>
Date: Thu, 7 Apr 2016 17:25:03 -0400
Subject: [PATCH 1/3] Make all event listeners passive where supported

See [the passive event listener explainer](https://github.com/WICG/EventListenerOptions/blob/gh-pages/explainer.md).  In practice we believe changing just this one script will have a measurable scroll performance improvement on the web.
---
 src/tracker/engaged_time.js | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/tracker/engaged_time.js b/src/tracker/engaged_time.js
index ab60971..10dc977 100644
--- a/src/tracker/engaged_time.js
+++ b/src/tracker/engaged_time.js
@@ -85,9 +85,17 @@ limitations under the License.
         root.focused = false;
     });
 
+    var supportsPassive = false;
+    try {
+        addEventListener("test", null, { get capture() { supportsPassive = true; } });
+    } catch(e) {}
+    var optionsOrCapture = false;
+    if (supportsPassive)
+        optionsOrCapture = {passive:true, capture:false}
+    
     var _buildListener = function(event_name, callback) {
         if (window.addEventListener) {
-            window.addEventListener(event_name, callback, false);
+            window.addEventListener(event_name, callback, optionsOrCapture);
         } else {
             document.attachEvent("on" + event_name, callback);
         }

From 7464608a06a9ff4df5e4c99043814b2d39326c72 Mon Sep 17 00:00:00 2001
From: Rick Byers <rbyers@chromium.org>
Date: Thu, 7 Apr 2016 19:26:38 -0400
Subject: [PATCH 2/3] Update engaged_time.js

---
 src/tracker/engaged_time.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/tracker/engaged_time.js b/src/tracker/engaged_time.js
index 10dc977..8edd50a 100644
--- a/src/tracker/engaged_time.js
+++ b/src/tracker/engaged_time.js
@@ -87,7 +87,7 @@ limitations under the License.
 
     var supportsPassive = false;
     try {
-        addEventListener("test", null, { get capture() { supportsPassive = true; } });
+        addEventListener("test", null, { get passive() { supportsPassive = true; } });
     } catch(e) {}
     var optionsOrCapture = false;
     if (supportsPassive)

From 3820123e17a630383ad1847d6c578c60a62ff311 Mon Sep 17 00:00:00 2001
From: Rick Byers <rbyers@chromium.org>
Date: Fri, 8 Apr 2016 12:14:14 -0400
Subject: [PATCH 3/3] Update engaged_time.js

---
 src/tracker/engaged_time.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/tracker/engaged_time.js b/src/tracker/engaged_time.js
index 8edd50a..1da622b 100644
--- a/src/tracker/engaged_time.js
+++ b/src/tracker/engaged_time.js
@@ -87,7 +87,9 @@ limitations under the License.
 
     var supportsPassive = false;
     try {
-        addEventListener("test", null, { get passive() { supportsPassive = true; } });
+        addEventListener("test", null, Object.defineProperty({}, 'passive', {get: function () {
+            supportsPassive = true;
+        }}));
     } catch(e) {}
     var optionsOrCapture = false;
     if (supportsPassive)