Fabric: Gating for new state reconciliation

Summary:
The change is gated by two QEs (iOS and Android).

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: mdvacca

Differential Revision: D21317797

fbshipit-source-id: 34bfd9546600d9cb3467bddfc61363a16683f81f

ReactCommon/fabric/mounting/ShadowTree.cpp

@@ -297,7 +297,7 @@ bool ShadowTree::tryCommit(
   }
 
   if (enableStateReconciliation) {
-    if (useNewApproachToStateReconciliation_) {
+    if (enableNewStateReconciliation_) {
       auto updatedNewRootShadowNode =
           progressState(*newRootShadowNode, *oldRootShadowNode);
       if (updatedNewRootShadowNode) {

ReactCommon/fabric/mounting/ShadowTree.h

@@ -71,6 +71,14 @@ class ShadowTree final {
 
   MountingCoordinator::Shared getMountingCoordinator() const;
 
+  /*
+   * Temporary.
+   * Do not use.
+   */
+  void setEnableNewStateReconciliation(bool value) {
+    enableNewStateReconciliation_ = value;
+  }
+
  private:
   RootShadowNode::Unshared cloneRootShadowNode(
       RootShadowNode::Shared const &oldRootShadowNode,
@@ -88,7 +96,7 @@ class ShadowTree final {
   mutable ShadowTreeRevision::Number revisionNumber_{
       0}; // Protected by `commitMutex_`.
   MountingCoordinator::Shared mountingCoordinator_;
-  bool useNewApproachToStateReconciliation_{true};
+  bool enableNewStateReconciliation_{false};
 };
 
 } // namespace react

ReactCommon/fabric/scheduler/Scheduler.cpp

@@ -80,6 +80,14 @@ Scheduler::Scheduler(
 
   delegate_ = delegate;
   uiManager_ = uiManager;
+
+#ifdef ANDROID
+  enableNewStateReconciliation_ = reactNativeConfig_->getBool(
+      "react_fabric:enable_new_state_reconciliation_android");
+#else
+  enableNewStateReconciliation_ = reactNativeConfig_->getBool(
+      "react_fabric:enable_new_state_reconciliation_ios");
+#endif
 }
 
 Scheduler::~Scheduler() {
@@ -141,6 +149,8 @@ void Scheduler::startSurface(
       *rootComponentDescriptor_,
       *uiManager_);
 
+  shadowTree->setEnableNewStateReconciliation(enableNewStateReconciliation_);
+
   auto uiManager = uiManager_;
 
   uiManager->getShadowTreeRegistry().add(std::move(shadowTree));

ReactCommon/fabric/scheduler/Scheduler.h

@@ -112,6 +112,7 @@ class Scheduler final : public UIManagerDelegate {
   std::shared_ptr<UIManager> uiManager_;
   std::shared_ptr<const ReactNativeConfig> reactNativeConfig_;
   EventDispatcher::Shared eventDispatcher_;
+  bool enableNewStateReconciliation_{false};
 };
 
 } // namespace react