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**Do you want to request a *feature* or report a *bug*?**
Bug.

**What is the current behavior?**
`<embed>` doesn't trigger `onLoad`

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:**

https://codesandbox.io/s/9yrqzw71xp

**What is the expected behavior?**
`<embed>` should trigger `onLoad`

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
16.8.6

import {DOCUMENT_NODE, DOCUMENT_FRAGMENT_NODE} from '../shared/HTMLNodeType';
import isCustomComponent from '../shared/isCustomComponent';
import possibleStandardNames from '../shared/possibleStandardNames';
import {validateProperties as validateARIAProperties} from '../shared/ReactDOMInvalidARIAHook';
import {validateProperties as validateInputProperties} from '../shared/ReactDOMNullInputValuePropHook';
import {validateProperties as validateUnknownProperties} from '../shared/ReactDOMUnknownPropertyHook';
import {enableEventAPI} from 'shared/ReactFeatureFlags';
let didWarnInvalidHydration = false;
let didWarnShadyDOM = false;
const DANGEROUSLY_SET_INNER_HTML = 'dangerouslySetInnerHTML';
const SUPPRESS_CONTENT_EDITABLE_WARNING = 'suppressContentEditableWarning';
const SUPPRESS_HYDRATION_WARNING = 'suppressHydrationWarning';
const HYDRATE_TOUCH_HIT_TARGET = 'hydrateTouchHitTarget';
const AUTOFOCUS = 'autoFocus';
const CHILDREN = 'children';
const STYLE = 'style';
const HTML = '__html';
const {html: HTML_NAMESPACE} = Namespaces;
let warnedUnknownTags;
let suppressHydrationWarning;
let validatePropertiesInDevelopment;
let warnForTextDifference;
let warnForPropDifference;
let warnForExtraAttributes;
let warnForInvalidEventListener;
let canDiffStyleForHydrationWarning;
let normalizeMarkupForTextOrAttribute;
let normalizeHTML;
if (__DEV__) {
  warnedUnknownTags = {