Fix startup race condition

Summary:
Currently Flipper.init is called as soon as the script loads.
However, if the store takes a bit longer than usual to get rehydrated, then this init call can get called before it has been set.

Fixing it by using a specific event instead of the generic `onload`.

Reviewed By: passy

Differential Revision: D17711399

fbshipit-source-id: fcaf9e5943bfd15359038b8e3722f11d7e06379b

src/init.tsx

@@ -88,4 +88,5 @@ persistStore(store, undefined, () => {
   dispatcher(store, logger);
   // make init function callable from outside
   window.Flipper.init = init;
+  window.dispatchEvent(new Event('flipper-store-ready'));
 });

static/index.dev.html

@@ -85,13 +85,10 @@
             openError('Script failure. Check Chrome console for more info.');
           };
 
-          script.onload = () => {
+          window.addEventListener('flipper-store-ready', () => global.Flipper.init());
-            global.Flipper.init();
-          };
 
           document.body.appendChild(script);
         }
-
         init();
       })();
     </script>

static/index.html

@@ -13,9 +13,9 @@
     <script>
       global.electronRequire = window.require;
     </script>
-    <script src="bundle.js"></script>
     <script>
-      global.Flipper.init();
+      window.addEventListener('flipper-store-ready', () => global.Flipper.init());
     </script>
+    <script src="bundle.js"></script>
   </body>
 </html>