Change the behavior to always fail childContextTypes if there is a method (#8391)

Even if that method returns falsy values.

scripts/fiber/tests-failing.txt

@@ -92,8 +92,6 @@ src/renderers/shared/stack/reconciler/__tests__/ReactComponentLifeCycle-test.js
 * should carry through each of the phases of setup
 
 src/renderers/shared/stack/reconciler/__tests__/ReactCompositeComponent-test.js
-* should warn about `forceUpdate` on unmounted components
-* should warn about `setState` on unmounted components
 * should warn about `setState` in render
 * should warn about `setState` in getChildContext
 * should update refs if shouldComponentUpdate gives false

scripts/fiber/tests-passing-except-dev.txt

@@ -162,6 +162,8 @@ src/renderers/shared/stack/reconciler/__tests__/ReactComponentLifeCycle-test.js
 * warns if findDOMNode is used inside render
 
 src/renderers/shared/stack/reconciler/__tests__/ReactCompositeComponent-test.js
+* should warn about `forceUpdate` on unmounted components
+* should warn about `setState` on unmounted components
 * should disallow nested render calls
 * should warn when mutated props are passed
 

src/renderers/shared/fiber/ReactFiberScheduler.js

@@ -760,7 +760,8 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) {
           scheduleWorkAtPriority(root, priorityLevel);
           return;
         } else {
-          throw new Error('Invalid root');
+          // TODO: Warn about setting state on an unmounted component.
+          return;
         }
       }
       fiber = fiber.return;

src/renderers/shared/stack/reconciler/ReactCompositeComponent.js

@@ -678,7 +678,7 @@ var ReactCompositeComponent = {
     var inst = this._instance;
     var childContext;
 
-    if (inst.getChildContext) {
+    if (typeof inst.getChildContext === 'function') {
       if (__DEV__) {
         ReactInstrumentation.debugTool.onBeginProcessingChildContext();
         try {
@@ -689,9 +689,7 @@ var ReactCompositeComponent = {
       } else {
         childContext = inst.getChildContext();
       }
-    }
 
-    if (childContext) {
       invariant(
         typeof Component.childContextTypes === 'object',
         '%s.getChildContext(): childContextTypes must be defined in order to ' +

src/renderers/shared/stack/reconciler/__tests__/ReactCompositeComponent-test.js

@@ -427,6 +427,7 @@ describe('ReactCompositeComponent', () => {
         return <div />;
       }
     }
+    Component.childContextTypes = {};
 
     expectDev(console.error.calls.count()).toBe(0);
     var instance = ReactDOM.render(<Component />, container);