React native event type fixes (#10627)

* Added invariant check for native dispatching an unsupported event type
This prevents a case of a silent failure when native dispatches an event that JavaScript does not know how to handle.

* Added iOS direct event type 'onSnapshotReady'
This is used for snapshot testing.

src/renderers/native/ReactNativeBridgeEventPlugin.js

@@ -14,6 +14,7 @@
 var EventPropagators = require('EventPropagators');
 var SyntheticEvent = require('SyntheticEvent');
 var ReactNativeEventTypes = require('ReactNativeEventTypes');
+var invariant = require('fbjs/lib/invariant');
 
 var customBubblingEventTypes = ReactNativeEventTypes.customBubblingEventTypes;
 var customDirectEventTypes = ReactNativeEventTypes.customDirectEventTypes;
@@ -44,6 +45,11 @@ var ReactNativeBridgeEventPlugin = {
   ): ?Object {
     var bubbleDispatchConfig = customBubblingEventTypes[topLevelType];
     var directDispatchConfig = customDirectEventTypes[topLevelType];
+    invariant(
+      bubbleDispatchConfig || directDispatchConfig,
+      'Unsupported top level event type "%s" dispatched',
+      topLevelType,
+    );
     var event = SyntheticEvent.getPooled(
       bubbleDispatchConfig || directDispatchConfig,
       targetInst,

src/renderers/native/ReactNativeEventTypes.js

@@ -284,6 +284,9 @@ const IOS_DIRECT_EVENT_TYPES = {
   topShouldStartLoadWithRequest: {
     registrationName: 'onShouldStartLoadWithRequest',
   },
+  topSnapshotReady: {
+    registrationName: 'onSnapshotReady',
+  },
   topStateChange: {
     registrationName: 'onStateChange',
   },