Add unstable_renderSubtreeIntoContainer and unstable_createPortal feature flags (#17880)

Author: trueadm

packages/react-dom/src/__tests__/ReactDOMFiber-test.js

@@ -13,6 +13,8 @@ const React = require('react');
 const ReactDOM = require('react-dom');
 const PropTypes = require('prop-types');
 
+const ReactFeatureFlags = require('shared/ReactFeatureFlags');
+
 describe('ReactDOMFiber', () => {
   let container;
 
@@ -247,30 +249,32 @@ describe('ReactDOMFiber', () => {
   });
 
   // TODO: remove in React 17
-  it('should support unstable_createPortal alias', () => {
-    const portalContainer = document.createElement('div');
+  if (!ReactFeatureFlags.disableUnstableCreatePortal) {
+    it('should support unstable_createPortal alias', () => {
+      const portalContainer = document.createElement('div');
 
-    expect(() =>
-      ReactDOM.render(
-        <div>
-          {ReactDOM.unstable_createPortal(<div>portal</div>, portalContainer)}
-        </div>,
-        container,
-      ),
-    ).toWarnDev(
-      'The ReactDOM.unstable_createPortal() alias has been deprecated, ' +
-        'and will be removed in React 17+. Update your code to use ' +
-        'ReactDOM.createPortal() instead. It has the exact same API, ' +
-        'but without the "unstable_" prefix.',
-      {withoutStack: true},
-    );
-    expect(portalContainer.innerHTML).toBe('<div>portal</div>');
-    expect(container.innerHTML).toBe('<div></div>');
+      expect(() =>
+        ReactDOM.render(
+          <div>
+            {ReactDOM.unstable_createPortal(<div>portal</div>, portalContainer)}
+          </div>,
+          container,
+        ),
+      ).toWarnDev(
+        'The ReactDOM.unstable_createPortal() alias has been deprecated, ' +
+          'and will be removed in React 17+. Update your code to use ' +
+          'ReactDOM.createPortal() instead. It has the exact same API, ' +
+          'but without the "unstable_" prefix.',
+        {withoutStack: true},
+      );
+      expect(portalContainer.innerHTML).toBe('<div>portal</div>');
+      expect(container.innerHTML).toBe('<div></div>');
 
-    ReactDOM.unmountComponentAtNode(container);
-    expect(portalContainer.innerHTML).toBe('');
-    expect(container.innerHTML).toBe('');
-  });
+      ReactDOM.unmountComponentAtNode(container);
+      expect(portalContainer.innerHTML).toBe('');
+      expect(container.innerHTML).toBe('');
+    });
+  }
 
   it('should render many portals', () => {
     const portalContainer1 = document.createElement('div');