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

bug

**What is the current behavior?**

The warning for a failure to initialize state when using `getDerivedStateFromProps` is not as clear as it could be.

This component produces the warning:
> MyComponent: Did not properly initialize state during construction. Expected state to be an object, but it was undefined.`

```js
class MyComponent extends React.Component {
  static getDerivedStateFromProps(nextProps, prevState) {
    return null;
  }
  render() {
    return <span>Foo</span>
  }
}
```

The warning can be resolved by adding `state = {}` either in the class definition or the constructor, or by not using `getDerivedStateFromProps`.

See https://github.com/reactjs/reactjs.org/issues/796 for more detail on why this warning message can be counter-intuitive.

Since the [warning is specific](https://github.com/facebook/react/blob/b548b3cd640dbd515f5d67dafc0216bb7ee0d796/packages/react-reconciler/src/ReactFiberClassComponent.js#L509-L510) to the use of `getDerivedStateFromProps` and not triggered by any other state or lifecycle methods, and state initialization isn't required for other state methods like `this.setState`, it would make sense to me to mention `getDerivedStateFromProps` explicitly in the warning.

Here's a proposal for a new warning message:
> MyComponent: Component state must be initialized when using getDerivedStateFromProps. Expected state to be an object, but it was undefined.

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

React >= 16.3.0

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */
import type {Fiber} from './ReactFiber';
import type {ExpirationTime} from './ReactFiberExpirationTime';
import React from 'react';
import {Update, Snapshot} from 'shared/ReactTypeOfSideEffect';
import {
  debugRenderPhaseSideEffects,
  debugRenderPhaseSideEffectsForStrictMode,
  warnAboutDeprecatedLifecycles,
} from 'shared/ReactFeatureFlags';
import ReactStrictModeWarnings from './ReactStrictModeWarnings';
import {isMounted} from 'react-reconciler/reflection';
import * as ReactInstanceMap from 'shared/ReactInstanceMap';
import shallowEqual from 'shared/shallowEqual';
import getComponentName from 'shared/getComponentName';
import invariant from 'shared/invariant';
import warningWithoutStack from 'shared/warningWithoutStack';
import {startPhaseTimer, stopPhaseTimer} from './ReactDebugFiberPerf';
import {StrictMode} from './ReactTypeOfMode';
import {
  enqueueUpdate,