[Fiber] Fix portal unmounting

scripts/fiber/tests-passing.txt

@@ -489,7 +489,8 @@ src/renderers/dom/fiber/__tests__/ReactDOMFiber-test.js
 * finds the first child when a component returns a fragment
 * finds the first child even when fragment is nested
 * finds the first child even when first child renders null
-* should render portal children
+* should render one portal
+* should render many portals
 * should render nested portals
 * should pass portal context when rendering subtree elsewhere
 * should update portal context if it changes due to setState

src/renderers/dom/fiber/__tests__/ReactDOMFiber-test.js

@@ -188,7 +188,27 @@ describe('ReactDOMFiber', () => {
   }
 
   if (ReactDOMFeatureFlags.useFiber) {
-    it('should render portal children', () => {
+    it('should render one portal', () => {
+      var portalContainer = document.createElement('div');
+
+      ReactDOM.render(
+        <div>
+          {ReactDOM.unstable_createPortal(
+            <div>portal</div>,
+            portalContainer
+          )}
+        </div>,
+        container
+      );
+      expect(portalContainer.innerHTML).toBe('<div>portal</div>');
+      expect(container.innerHTML).toBe('<div></div>');
+
+      ReactDOM.unmountComponentAtNode(container);
+      expect(portalContainer.innerHTML).toBe('');
+      expect(container.innerHTML).toBe('');
+    });
+
+    it('should render many portals', () => {
       var portalContainer1 = document.createElement('div');
       var portalContainer2 = document.createElement('div');
 

src/renderers/shared/fiber/ReactFiberCommitWork.js

@@ -283,6 +283,11 @@ module.exports = function<T, P, I, TI, C>(
         commitNestedUnmounts(current.stateNode);
         return;
       }
+      case Portal: {
+        // TODO: this is recursive.
+        commitDeletion(current);
+        return;
+      }
     }
   }