Release fix for race condition on startSurface

Summary:
This bug doesn't reproduce anymore in v301+. MC has been enabled since december

https://www.internalfb.com/intern/logview/details/facebook_android_javascripterrors/419f8892e7b1a02f205810219ddfc299/trends?selected-logview-tab=All%20Traces&drillstate={%22start%22:%22Thu,%2028%20Jan%202021%2000:59:54%20-0800%22,%22end%22:%22Thu,%2011%20Feb%202021%2000:59:54%20-0800%22,%22constraints%22:[{%22col%22:%22mid%22,%22op%22:%22==%22,%22vals%22:[%22419f8892e7b1a02f205810219ddfc299%22]}],%22context%22:%22facebook_android_javascripterrors%22,%22metric%22:%22count%22}

changelog: [internal] internal

Reviewed By: ShikaSD

Differential Revision: D26398484

fbshipit-source-id: ca85ca211f1a38aa2691f150956a27c878d243bc

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -803,9 +803,7 @@ public void showDevOptionsDialog() {
   @ThreadConfined(UI)
   private void clearReactRoot(ReactRoot reactRoot) {
     UiThreadUtil.assertOnUiThread();
-    if (ReactFeatureFlags.enableStartSurfaceRaceConditionFix) {
-      reactRoot.getState().compareAndSet(ReactRoot.STATE_STARTED, ReactRoot.STATE_STOPPED);
-    }
+    reactRoot.getState().compareAndSet(ReactRoot.STATE_STARTED, ReactRoot.STATE_STOPPED);
     ViewGroup rootViewGroup = reactRoot.getRootViewGroup();
     rootViewGroup.removeAllViews();
     rootViewGroup.setId(View.NO_ID);
@@ -826,12 +824,7 @@ public void attachRootView(ReactRoot reactRoot) {
     // Calling clearReactRoot is necessary to initialize the Id on reactRoot
     // This is necessary independently if the RN Bridge has been initialized or not.
     // Ideally reactRoot should be initialized with id == NO_ID
-    if (ReactFeatureFlags.enableStartSurfaceRaceConditionFix) {
-      if (mAttachedReactRoots.add(reactRoot)) {
-        clearReactRoot(reactRoot);
-      }
-    } else {
-      mAttachedReactRoots.add(reactRoot);
+    if (mAttachedReactRoots.add(reactRoot)) {
       clearReactRoot(reactRoot);
     }
 
@@ -840,8 +833,7 @@ public void attachRootView(ReactRoot reactRoot) {
     // reactRoot reactRoot list.
     ReactContext currentContext = getCurrentReactContext();
     if (mCreateReactContextThread == null && currentContext != null) {
-      if (!ReactFeatureFlags.enableStartSurfaceRaceConditionFix
-          || reactRoot.getState().compareAndSet(ReactRoot.STATE_STOPPED, ReactRoot.STATE_STARTED)) {
+      if (reactRoot.getState().compareAndSet(ReactRoot.STATE_STOPPED, ReactRoot.STATE_STARTED)) {
         attachRootViewToInstance(reactRoot);
       }
     }
@@ -1110,10 +1102,7 @@ private void setupReactContext(final ReactApplicationContext reactContext) {
 
       ReactMarker.logMarker(ATTACH_MEASURED_ROOT_VIEWS_START);
       for (ReactRoot reactRoot : mAttachedReactRoots) {
-        if (!ReactFeatureFlags.enableStartSurfaceRaceConditionFix
-            || reactRoot
-                .getState()
-                .compareAndSet(ReactRoot.STATE_STOPPED, ReactRoot.STATE_STARTED)) {
+        if (reactRoot.getState().compareAndSet(ReactRoot.STATE_STOPPED, ReactRoot.STATE_STARTED)) {
           attachRootViewToInstance(reactRoot);
         }
       }

ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -54,12 +54,6 @@ public class ReactFeatureFlags {
   /** Feature flag to configure eager initialization of Fabric */
   public static boolean eagerInitializeFabric = false;
 
-  /**
-   * Fixes race-condition in the initialization of RN surface. TODO T78832286: remove this flag once
-   * we verify the fix is correct in production
-   */
-  public static boolean enableStartSurfaceRaceConditionFix = false;
-
   /** Enables Static ViewConfig in RN Android native code. */
   public static boolean enableExperimentalStaticViewConfigs = false;