Set up experiment to dispatch promise methods asynchronously to Nativ…

…eModules thread

Summary:
TurboModule methods that return promises are synchronously run on the JavaScript thread. Back in D22489338 (9c35b5b), we wrote code to make them dispatch on the NativeModules thread. That code, however, was just left disabled. In this diff, I wire up the TurboModules infra to a MobileConfig, which should allow us to assess the performance impact of async dispatch of promise methods to the NativeModules thread in production, before we roll it out more widely.

Changelog: [Internal]

Reviewed By: fkgozali

Differential Revision: D24685389

fbshipit-source-id: 8ceb2e6effc125abecfa76e5e90bd310676aefc9

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

@@ -23,6 +23,9 @@ public class ReactFeatureFlags {
    */
   public static volatile boolean useTurboModules = false;
 
+  /** Should we dispatch TurboModule methods with promise returns to the NativeModules thread? */
+  public static volatile boolean enableTurboModulePromiseAsyncDispatch = false;
+
   /*
    * This feature flag enables logs for Fabric
    */

ReactAndroid/src/main/java/com/facebook/react/turbomodule/core/TurboModuleManager.java

@@ -17,6 +17,7 @@
 import com.facebook.react.bridge.JSIModule;
 import com.facebook.react.bridge.JavaScriptContextHolder;
 import com.facebook.react.bridge.NativeModule;
+import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.turbomodule.core.interfaces.CallInvokerHolder;
 import com.facebook.react.turbomodule.core.interfaces.TurboModule;
 import com.facebook.react.turbomodule.core.interfaces.TurboModuleRegistry;
@@ -60,7 +61,7 @@ public TurboModuleManager(
             (CallInvokerHolderImpl) jsCallInvokerHolder,
             (CallInvokerHolderImpl) nativeCallInvokerHolder,
             delegate,
-            false);
+            ReactFeatureFlags.enableTurboModulePromiseAsyncDispatch);
     installJSIBindings();
 
     mEagerInitModuleNames =