Fix memory leak hotspots (#5116)

- render: clear the root Fragment's props.children after commit so replaced vnode generations are not retained

- unmount: clear component._globalContext with the other component references

(cherry picked from commit bd0302d)

Author: JoviDeCroock

src/diff/index.js

@@ -717,7 +717,7 @@ export function unmount(vnode, parentVNode, skipRemove) {
 			}
 		}
 
-		r._parentDom = NULL;
+		r._parentDom = r._globalContext = NULL;
 	}
 
 	if ((r = vnode._children)) {

src/render.js

@@ -56,6 +56,9 @@ export function render(vnode, parentDom) {
 
 	// Flush all queued effects
 	commitRoot(commitQueue, parentDom._children, refQueue);
+
+	// The live children are tracked on _children after diffing.
+	parentDom._children.props.children = NULL;
 }
 
 /**

test/browser/render.test.jsx

@@ -227,6 +227,30 @@ describe('render()', () => {
 		expect(scratch.innerHTML).to.equal('<span class="hello">Hello!</span>');
 	});
 
+	it('should not keep the root input vnode in props.children', () => {
+		let update;
+		class App extends Component {
+			constructor(props) {
+				super(props);
+				this.state = { value: 'a' };
+				update = this.setState.bind(this);
+			}
+
+			render() {
+				return <button>{this.state.value}</button>;
+			}
+		}
+
+		render(<App />, scratch);
+		let firstAppVNode = scratch._children._children[0];
+
+		update({ value: 'b' });
+		rerender();
+
+		expect(scratch._children._children[0]).to.not.equal(firstAppVNode);
+		expect(scratch._children.props.children).to.equal(null);
+	});
+
 	it('should nest empty nodes', () => {
 		render(
 			<div>