**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

import {validateProperties as validateInputProperties} from '../shared/ReactDOMNullInputValuePropHook';
import {validateProperties as validateUnknownProperties} from '../shared/ReactDOMUnknownPropertyHook';
type ReactNode = string | number | ReactElement;
type FlatReactChildren = Array<null | ReactNode>;
type toArrayType = (children: mixed) => FlatReactChildren;
const toArray = ((React.Children.toArray: any): toArrayType);
let currentDebugStacks = [];
let ReactDebugCurrentFrame;
let prevGetCurrentStackImpl = null;
let getCurrentServerStackImpl = () => '';
let describeStackFrame = element => '';
let validatePropertiesInDevelopment = (type, props) => {};
let pushCurrentDebugStack = (stack: Array<Frame>) => {};
let pushElementToDebugStack = (element: ReactElement) => {};
let popCurrentDebugStack = () => {};
if (__DEV__) {
  ReactDebugCurrentFrame = ReactSharedInternals.ReactDebugCurrentFrame;
  validatePropertiesInDevelopment = function(type, props) {
    validateARIAProperties(type, props);
    validateInputProperties(type, props);
    validateUnknownProperties(type, props,  false);
  };
  describeStackFrame = function(element): string {
    const source = element._source;
    const type = element.type;
    const name = getComponentName(type);
    const ownerName = null;
    return describeComponentFrame(name, source, ownerName);
  };
  pushCurrentDebugStack = function(stack: Array<Frame>) {