Add areChildrenOffscreen to host config

Renderers can determine whether a node's children are offscreen based on
the host component's props. If so, they are given OffscreenPriority.

useSyncScheduling takes precedence.

src/renderers/art/ReactARTFiber.js

@@ -503,6 +503,10 @@ const ARTRenderer = ReactFiberReconciler({
     // Noop
   },
 
+  areChildrenOffscreen(props : Props) {
+    return false;
+  },
+
   getRootHostContext() {
     return emptyObject;
   },

src/renderers/dom/fiber/ReactDOMFiber.js

@@ -69,6 +69,7 @@ type Container = Element;
 type Props = {
   autoFocus ?: boolean,
   children ?: mixed,
+  hidden ?: boolean,
 };
 type Instance = Element;
 type TextInstance = Text;
@@ -286,6 +287,10 @@ var DOMRenderer = ReactFiberReconciler({
     domElement.textContent = '';
   },
 
+  areChildrenOffscreen(props : Props) : boolean {
+    return Boolean(props.hidden);
+  },
+
   createTextInstance(
     text : string,
     rootContainerInstance : Container,

src/renderers/native/ReactNativeFiber.js

@@ -343,6 +343,10 @@ const NativeRenderer = ReactFiberReconciler({
     // Noop
   },
 
+  areChildrenOffscreen(props : Props) : boolean {
+    return false;
+  },
+
   scheduleAnimationCallback: global.requestAnimationFrame,
 
   scheduleDeferredCallback: global.requestIdleCallback,

src/renderers/noop/ReactNoop.js

@@ -35,7 +35,7 @@ var scheduledAnimationCallback = null;
 var scheduledDeferredCallback = null;
 
 type Container = { rootID: string, children: Array<Instance | TextInstance> };
-type Props = { prop: any };
+type Props = { prop: any, hidden ?: boolean };
 type Instance = {| type: string, id: number, children: Array<Instance | TextInstance>, prop: any |};
 type TextInstance = {| text: string, id: number |};
 
@@ -101,6 +101,10 @@ var NoopRenderer = ReactFiberReconciler({
 
   resetTextContent(instance : Instance) : void {},
 
+  areChildrenOffscreen(props : Props) : boolean {
+    return Boolean(props.hidden);
+  },
+
   createTextInstance(
     text : string,
     rootContainerInstance : Container,

src/renderers/shared/fiber/ReactFiberBeginWork.js

@@ -77,7 +77,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
   getPriorityContext : () => PriorityLevel,
 ) {
 
-  const { shouldSetTextContent, useSyncScheduling } = config;
+  const { shouldSetTextContent, useSyncScheduling, areChildrenOffscreen } = config;
 
   const {
     pushHostContext,
@@ -358,7 +358,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
       }
     } else if (nextProps === null || memoizedProps === nextProps) {
       if (!useSyncScheduling &&
-          memoizedProps.hidden &&
+          areChildrenOffscreen(memoizedProps) &&
           workInProgress.pendingWorkPriority !== OffscreenPriority) {
         // This subtree still has work, but it should be deprioritized so we need
         // to bail out and not do any work yet.
@@ -400,7 +400,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
     markRef(current, workInProgress);
 
     if (!useSyncScheduling &&
-        nextProps.hidden &&
+        areChildrenOffscreen(nextProps) &&
         workInProgress.pendingWorkPriority !== OffscreenPriority) {
       // If this host component is hidden, we can bail out on the children.
       // We'll rerender the children later at the lower priority.

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -83,6 +83,7 @@ export type HostConfig<T, P, I, TI, PI, C, CX, PL> = {
 
   shouldSetTextContent(props : P) : boolean,
   resetTextContent(instance : I) : void,
+  areChildrenOffscreen(props : P) : boolean,
 
   createTextInstance(
     text : string,

src/renderers/testing/ReactTestRendererFiber.js

@@ -150,6 +150,10 @@ var TestRenderer = ReactFiberReconciler({
     // noop
   },
 
+  areChildrenOffscreen(props : Props) : boolean {
+    return false;
+  },
+
   createTextInstance(
     text : string,
     rootContainerInstance : Container,