expose AppRegistry.getRegistry() for app specific handling

Summary: Add simple `getRegistry()` so that add can do some custom handling of the registered components, if appropriate.

Reviewed By: shergin

Differential Revision: D4550600

fbshipit-source-id: 367c66b9fddfe4cc81cbc32a7a6043215e0df666

Libraries/ReactNative/AppRegistry.js

@@ -43,6 +43,10 @@ type Runnable = {
 type Runnables = {
   [appKey: string]: Runnable,
 };
+type Registry = {
+  sections: Array<string>,
+  runnables: Runnables,
+};
 
 const runnables: Runnables = {};
 let runCount = 1;
@@ -128,6 +132,13 @@ const AppRegistry = {
     return runnables[appKey];
   },
 
+  getRegistry(): Registry {
+    return {
+      sections: AppRegistry.getSectionKeys(),
+      runnables: {...runnables},
+    };
+  },
+
   runApplication(appKey: string, appParameters: any): void {
     const msg =
       'Running application "' + appKey + '" with appParams: ' +