import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

testing/web-platform/tests/eventsource/format-field-id.htm

@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>EventSource: Last-Event-ID</title>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+  </head>
+  <body>
+    <div id="log"></div>
+    <script>
+      var test = async_test()
+      test.step(function() {
+        var source = new EventSource("resources/last-event-id.py"),
+            seenhello = false
+        source.onmessage = function(e) {
+          test.step(function() {
+            if(e.data == "hello" && !seenhello) {
+              seenhello = true
+              assert_equals(e.lastEventId, "…")
+            } else if(seenhello) {
+              assert_equals("…", e.data)
+              assert_equals("…", e.lastEventId)
+              source.close()
+              test.done()
+            } else
+              assert_unreached()
+          })
+        }
+      })
+    </script>
+  </body>
+</html>
+