<s>I'm going to revert</s> I have reverted https://github.com/facebook/react/pull/5947 because it's [very confusing](https://mobile.twitter.com/ReactStudent/status/1018749513572368384) to see Proxies in the console. The warning is just not worth the debugging impediment.

In the future, we should consider sealing or preventing extensions to pooled events (if we're not getting rid of pooling altogether, that is). But that would be a breaking change.
* them back into the pool. This allows a way to hold onto a reference that
   * won't be added back into the pool.
   */
  persist: function() {
    this.isPersistent = functionThatReturnsTrue;
  },
  /**
   * Checks if this event should be released back into the pool.
   *
   * @return {boolean} True if this should not be released, false otherwise.
   */
  isPersistent: functionThatReturnsFalse,
  /**
   * `PooledClass` looks for `destructor` on each instance it releases.
   */
  destructor: function() {
    const Interface = this.constructor.Interface;
    for (const propName in Interface) {
      if (__DEV__) {
        Object.defineProperty(
          this,
          propName,
          getPooledWarningPropertyDefinition(propName, Interface[propName]),
        );
      } else {
        this[propName] = null;
      }
    }
    for (let i = 0; i < shouldBeReleasedProperties.length; i++) {
      this[shouldBeReleasedProperties[i]] = null;