diff --git a/element-timing/background-image-data-uri.html b/element-timing/background-image-data-uri.html
index 16d6dfcba037f7..3cac0f56db860c 100644
--- a/element-timing/background-image-data-uri.html
+++ b/element-timing/background-image-data-uri.html
@@ -18,6 +18,9 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/background-image-multiple-elements.html b/element-timing/background-image-multiple-elements.html
index 22b4158cbe7289..a4ad83dbae069f 100644
--- a/element-timing/background-image-multiple-elements.html
+++ b/element-timing/background-image-multiple-elements.html
@@ -23,6 +23,9 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     let beforeRender = performance.now();
     let numObservedElements = 0;
     let observedDiv1 = false;
diff --git a/element-timing/background-image-stretched.html b/element-timing/background-image-stretched.html
index 28c35539824525..930b4cef8eb21b 100644
--- a/element-timing/background-image-stretched.html
+++ b/element-timing/background-image-stretched.html
@@ -18,6 +18,9 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/buffer-before-onload.html b/element-timing/buffer-before-onload.html
index 03c7048be1134b..88a641bbb66681 100644
--- a/element-timing/buffer-before-onload.html
+++ b/element-timing/buffer-before-onload.html
@@ -14,6 +14,9 @@
   the performance timeline.
   */
   async_test(function(t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     beforeRender = performance.now();
     const img = document.createElement('img');
     img.src = 'resources/square20.jpg';
diff --git a/element-timing/cross-origin-element.sub.html b/element-timing/cross-origin-element.sub.html
index 0af0ae96413eb8..40a97056c2bfba 100644
--- a/element-timing/cross-origin-element.sub.html
+++ b/element-timing/cross-origin-element.sub.html
@@ -12,6 +12,9 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     let img;
     const pathname = 'http://{{domains[www]}}:{{ports[http][1]}}'
           + '/element-timing/resources/square100.png';
diff --git a/element-timing/cross-origin-iframe-element.sub.html b/element-timing/cross-origin-iframe-element.sub.html
index a369d25bd43c65..7296cfccfda606 100644
--- a/element-timing/cross-origin-iframe-element.sub.html
+++ b/element-timing/cross-origin-iframe-element.sub.html
@@ -7,6 +7,9 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done((entryList) => {
         assert_unreached("We should not observe a cross origin element.");
diff --git a/element-timing/disconnect-image.html b/element-timing/disconnect-image.html
index 4ee0516fffecfe..82e7461b0417fb 100644
--- a/element-timing/disconnect-image.html
+++ b/element-timing/disconnect-image.html
@@ -9,6 +9,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/image-TAO-wildcard.sub.html b/element-timing/image-TAO-wildcard.sub.html
index 4ec8aa7d8dad99..3af893a9890410 100644
--- a/element-timing/image-TAO-wildcard.sub.html
+++ b/element-timing/image-TAO-wildcard.sub.html
@@ -12,6 +12,9 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     let beforeRender;
     let img;
     const img_src = 'http://{{domains[www]}}:{{ports[http][1]}}/element-timing/'
diff --git a/element-timing/image-carousel.html b/element-timing/image-carousel.html
index 404eca3b208cd0..39d9f0195c6ba1 100644
--- a/element-timing/image-carousel.html
+++ b/element-timing/image-carousel.html
@@ -26,6 +26,9 @@
 
 <script>
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const beforeRenderTimes = [];
     let entry_count = 0;
     const entry_count_per_element = [0, 0];
diff --git a/element-timing/image-clipped-svg.html b/element-timing/image-clipped-svg.html
index 3007bf726a6812..1e9971c8a8df75 100644
--- a/element-timing/image-clipped-svg.html
+++ b/element-timing/image-clipped-svg.html
@@ -7,6 +7,9 @@
 <script>
 let beforeRender;
 async_test(function (t) {
+  if (!window.PerformanceElementTiming) {
+    assert_unreached("PerformanceElementTiming is not implemented");
+  }
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/image-data-uri.html b/element-timing/image-data-uri.html
index 2b5d04e45a3f4c..e698bcf1a5d7f5 100644
--- a/element-timing/image-data-uri.html
+++ b/element-timing/image-data-uri.html
@@ -16,6 +16,9 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/image-not-added.html b/element-timing/image-not-added.html
index 59a254e9f179b1..e65d1814b0e759 100644
--- a/element-timing/image-not-added.html
+++ b/element-timing/image-not-added.html
@@ -5,6 +5,9 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(() => {
         // The image should not have caused an entry, so fail test.
diff --git a/element-timing/image-not-fully-visible.html b/element-timing/image-not-fully-visible.html
index 57162491a7927d..105bb55ebc0a3a 100644
--- a/element-timing/image-not-fully-visible.html
+++ b/element-timing/image-not-fully-visible.html
@@ -14,6 +14,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/image-rect-iframe.html b/element-timing/image-rect-iframe.html
index f0511308c7192b..7441405d7475b4 100644
--- a/element-timing/image-rect-iframe.html
+++ b/element-timing/image-rect-iframe.html
@@ -11,6 +11,9 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
   async_test((t) => {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     on_event(window, 'message', e => {
       assert_equals(e.data.length, 1);
       assert_equals(e.data.entryType, 'element');
diff --git a/element-timing/image-with-css-scale.html b/element-timing/image-with-css-scale.html
index bdffdb26b29e50..5c15daabe13dda 100644
--- a/element-timing/image-with-css-scale.html
+++ b/element-timing/image-with-css-scale.html
@@ -21,6 +21,9 @@
 <script>
   const beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/image-with-rotation.html b/element-timing/image-with-rotation.html
index 4433ecbc5f1146..c545becd19ba96 100644
--- a/element-timing/image-with-rotation.html
+++ b/element-timing/image-with-rotation.html
@@ -21,6 +21,9 @@
 <script>
   const beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/images-repeated-resource.html b/element-timing/images-repeated-resource.html
index fbb2d6a12cd39e..9bc8b5f45e4add 100644
--- a/element-timing/images-repeated-resource.html
+++ b/element-timing/images-repeated-resource.html
@@ -21,6 +21,9 @@
   const pathname = window.location.href.substring(0, index) +
       '/resources/square100.png';
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func(function(entryList) {
         entryList.getEntries().forEach(entry => {
diff --git a/element-timing/invisible-images.html b/element-timing/invisible-images.html
index 50aa6d13a9a5bf..eb53cd7c2a692c 100644
--- a/element-timing/invisible-images.html
+++ b/element-timing/invisible-images.html
@@ -16,6 +16,9 @@
 </style>
 <script>
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(() => {
         // The image should not have caused an entry, so fail test.
diff --git a/element-timing/multiple-background-images.html b/element-timing/multiple-background-images.html
index f3fbe767303f91..a762ed13396124 100644
--- a/element-timing/multiple-background-images.html
+++ b/element-timing/multiple-background-images.html
@@ -18,6 +18,9 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     let numObservedElements = 0;
     let observedCircle = false;
     let observedSquare = false;
diff --git a/element-timing/observe-background-image.html b/element-timing/observe-background-image.html
index 680c5e475aad49..c642264a19a89b 100644
--- a/element-timing/observe-background-image.html
+++ b/element-timing/observe-background-image.html
@@ -18,6 +18,9 @@
 <script>
   let beforeRender = performance.now();
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/observe-child-element.html b/element-timing/observe-child-element.html
index 9166a4b0e6d129..33e92a9abddd02 100644
--- a/element-timing/observe-child-element.html
+++ b/element-timing/observe-child-element.html
@@ -12,6 +12,9 @@
 <script src="resources/element-timing-helpers.js"></script>
 <script>
   async_test((t) => {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done((entryList) => {
         assert_unreached("Should not have received an entry!");
diff --git a/element-timing/observe-elementtiming.html b/element-timing/observe-elementtiming.html
index 73f93519cdaecd..0c67130dcc356e 100644
--- a/element-timing/observe-elementtiming.html
+++ b/element-timing/observe-elementtiming.html
@@ -14,6 +14,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/observe-large-image.html b/element-timing/observe-large-image.html
index 13fc71bc4e3316..e907452d82f2ce 100644
--- a/element-timing/observe-large-image.html
+++ b/element-timing/observe-large-image.html
@@ -14,6 +14,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/observe-multiple-images.html b/element-timing/observe-multiple-images.html
index b9e82ed10b1c01..8a5fa0bb89a31f 100644
--- a/element-timing/observe-multiple-images.html
+++ b/element-timing/observe-multiple-images.html
@@ -22,6 +22,9 @@
 <script>
   let beforeRender, image1Observed=0, image2Observed=0, image3Observed=0;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const index = window.location.href.lastIndexOf('/');
     const observer = new PerformanceObserver(
       t.step_func(function(entryList) {
diff --git a/element-timing/observe-shadow-image.html b/element-timing/observe-shadow-image.html
index a4d21bea808923..4309196cddcdca 100644
--- a/element-timing/observe-shadow-image.html
+++ b/element-timing/observe-shadow-image.html
@@ -14,6 +14,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/observe-svg-image.html b/element-timing/observe-svg-image.html
index c3c178e9b64775..29fec392a993b7 100644
--- a/element-timing/observe-svg-image.html
+++ b/element-timing/observe-svg-image.html
@@ -7,6 +7,9 @@
 <script>
 let beforeRender;
 async_test(function (t) {
+  if (!window.PerformanceElementTiming) {
+    assert_unreached("PerformanceElementTiming is not implemented");
+  }
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/observe-video-poster.html b/element-timing/observe-video-poster.html
index 500fcedcccf268..9f82478ea27779 100644
--- a/element-timing/observe-video-poster.html
+++ b/element-timing/observe-video-poster.html
@@ -7,6 +7,9 @@
 <script>
 let beforeRender;
 async_test(function (t) {
+  if (!window.PerformanceElementTiming) {
+    assert_unreached("PerformanceElementTiming is not implemented");
+  }
   const observer = new PerformanceObserver(
     t.step_func_done(function(entryList) {
       assert_equals(entryList.getEntries().length, 1);
diff --git a/element-timing/progressively-loaded-image.html b/element-timing/progressively-loaded-image.html
index c534621ccf86ae..a55c5896f2acdc 100644
--- a/element-timing/progressively-loaded-image.html
+++ b/element-timing/progressively-loaded-image.html
@@ -14,6 +14,9 @@
   let numInitial = 75;
   let sleep = 500;
   async_test(function(t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const img_src = 'resources/progressive-image.py?name=square20.jpg&numInitial='
       + numInitial + '&sleep=' + sleep;
     const observer = new PerformanceObserver(
diff --git a/element-timing/rectangular-image.html b/element-timing/rectangular-image.html
index a1af9616ea115a..0b44c4fdd92123 100644
--- a/element-timing/rectangular-image.html
+++ b/element-timing/rectangular-image.html
@@ -14,6 +14,9 @@
   let beforeRender;
   let img;
   async_test(function (t) {
+    if (!window.PerformanceElementTiming) {
+      assert_unreached("PerformanceElementTiming is not implemented");
+    }
     const observer = new PerformanceObserver(
       t.step_func_done(function(entryList) {
         assert_equals(entryList.getEntries().length, 1);