Experiment with HostFunction caching in TurboModules

Summary:
Enables two new experiments (and the current behaviour as default) to speed up access to TurboModule methods from JS.

1) HostObject - Current behaviour
2) Prototype - Connect the TM HostObject via `__proto__`, and cache any methods accessed on the wrapper object.
3) Eager - Eagerly store all methods on the wrapper object, do not expose the HostObject to JS at all (TurboModules no longer need to be HostObjects in this scenario)

Changelog: [Internal]

Reviewed By: JoshuaGross, rubennorte, mdvacca

Differential Revision: D36590018

fbshipit-source-id: c9565eb239eb6aeee0f06b581ff8cd72a92073fc

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

@@ -116,4 +116,15 @@ public class ReactFeatureFlags {
 
   /** Feature Flag to control RN Android scrollEventThrottle prop. */
   public static boolean enableScrollEventThrottle = false;
+
+  /**
+   * Feature flag that controls how turbo modules are exposed to JS
+   *
+   * <ul>
+   *   <li>0 = as a HostObject
+   *   <li>1 = as a plain object, backed with a HostObject as prototype
+   *   <li>2 = as a plain object, with all methods eagerly configured
+   * </ul>
+   */
+  public static int turboModuleBindingMode = 0;
 }

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

@@ -20,6 +20,17 @@
 namespace facebook {
 namespace react {
 
+constexpr static auto ReactFeatureFlagsJavaDescriptor =
+    "com/facebook/react/config/ReactFeatureFlags";
+
+static int getFeatureFlagValue(const char *name) {
+  static const auto reactFeatureFlagsJavaDescriptor =
+      jni::findClassStatic(ReactFeatureFlagsJavaDescriptor);
+  const auto field =
+      reactFeatureFlagsJavaDescriptor->getStaticField<jint>(name);
+  return reactFeatureFlagsJavaDescriptor->getStaticFieldValue(field);
+}
+
 TurboModuleManager::TurboModuleManager(
     jni::alias_ref<TurboModuleManager::javaobject> jThis,
     RuntimeExecutor runtimeExecutor,
@@ -169,8 +180,13 @@ void TurboModuleManager::installJSIBindings() {
       return nullptr;
     };
 
+    TurboModuleBindingMode bindingMode = static_cast<TurboModuleBindingMode>(
+        getFeatureFlagValue("turboModuleBindingMode"));
     TurboModuleBinding::install(
-        runtime, std::move(turboModuleProvider), longLivedObjectCollection_);
+        runtime,
+        std::move(turboModuleProvider),
+        bindingMode,
+        longLivedObjectCollection_);
   });
 }