Allow bridge delegate to specify whether to use custom JSC wrapper

Reviewed By: mhorowitz

Differential Revision: D4197657

fbshipit-source-id: 09e050f802b41c9a7016456c25381018b2123553

React/Base/RCTBridgeDelegate.h

@@ -82,6 +82,15 @@
  */
 - (BOOL)shouldBridgeInitializeNativeModulesSynchronously:(RCTBridge *)bridge;
 
+/**
+ * Configure whether the JSCExecutor created should use the system JSC API or
+ * alternative hooks provided. When returning YES from this method, you must have
+ * previously called facebook::react::setCustomJSCWrapper.
+ *
+ * @experimental
+ */
+- (BOOL)shouldBridgeUseCustomJSC:(RCTBridge *)bridge;
+
 /**
  * The bridge will automatically attempt to load the JS source code from the
  * location specified by the `sourceURLForBridge:` method, however, if you want

ReactCommon/cxxreact/JSCExecutor.cpp

@@ -216,7 +216,15 @@ void JSCExecutor::setContextName(const std::string& name) {
 void JSCExecutor::initOnJSVMThread() throw(JSException) {
   SystraceSection s("JSCExecutor.initOnJSVMThread");
 
+  #if defined(__APPLE__)
+  const bool useCustomJSC = m_jscConfig.getDefault("UseCustomJSC", false).getBool();
+  if (useCustomJSC) {
+    JSC_configureJSCForIOS(true);
+  }
+  #else
   const bool useCustomJSC = false;
+  #endif
+
   #if defined(WITH_FB_JSC_TUNING) && defined(__ANDROID__)
   configureJSCForAndroid(m_jscConfig);
   #endif