Expose way for native modules to modify JSC context

Reviewed By: svcscm

Differential Revision: D2933197

fb-gh-sync-id: 32eb943ab341804343bbcadd29f0377fccf75de6
shipit-source-id: 32eb943ab341804343bbcadd29f0377fccf75de6

React/Executors/RCTJSCExecutor.h

@@ -16,6 +16,15 @@
  */
 RCT_EXTERN NSString *const RCTJSCThreadName;
 
+/**
+ * This notification fires on the JS thread immediately after a `JSContext`
+ * is fully initialized, but before the JS bundle has been loaded. The object
+ * of this notification is the `JSContext`. Native modules should listen for
+ * notification only if they need to install custom functionality into the
+ * context. Note that this notification won't fire when debugging in Chrome.
+ */
+RCT_EXTERN NSString *const RCTJavaScriptContextCreatedNotification;
+
 /**
  * Uses a JavaScriptCore context as the execution engine.
  */

React/Executors/RCTJSCExecutor.m

@@ -28,6 +28,8 @@
 
 NSString *const RCTJSCThreadName = @"com.facebook.React.JavaScript";
 
+NSString *const RCTJavaScriptContextCreatedNotification = @"RCTJavaScriptContextCreatedNotification";
+
 static NSString *const RCTJSCProfilerEnabledDefaultsKey = @"RCTJSCProfilerEnabled";
 
 @interface RCTJavaScriptContext : NSObject <RCTInvalidating>
@@ -332,7 +334,16 @@ static void RCTInstallJSCProfiler(RCTBridge *bridge, JSContextRef context)
   }];
 
   [self executeBlockOnJavaScriptQueue:^{
-    RCTInstallJSCProfiler(_bridge, self.context.ctx);
+    RCTJSCExecutor *strongSelf = weakSelf;
+    if (!strongSelf.valid) {
+      return;
+    }
+
+    JSContext *context = strongSelf.context.context;
+    RCTInstallJSCProfiler(_bridge, context.JSGlobalContextRef);
+
+    [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptContextCreatedNotification
+                                                        object:context];
   }];
 
   for (NSString *event in @[RCTProfileDidStartProfiling, RCTProfileDidEndProfiling]) {