[admob] move native component to singleton

lib/modules/admob/AdMobComponent.js

@@ -13,13 +13,26 @@ const adMobPropTypes = {
   unitId: PropTypes.string.isRequired,
   request: PropTypes.object,
   video: PropTypes.object,
+};
+Object.keys(EventTypes).forEach((eventType) => {
+  adMobPropTypes[eventType] = PropTypes.func;
+});
+Object.keys(NativeExpressEventTypes).forEach((eventType) => {
+  adMobPropTypes[eventType] = PropTypes.func;
+});
+
+const nativeComponents = {};
+
+function getNativeComponent(name) {
+  if (nativeComponents[name]) return nativeComponents[name];
+  const component = requireNativeComponent(name, AdMobComponent, {
+    nativeOnly: {
+      onBannerEvent: true,
+    },
+  });
+  nativeComponents[name] = component;
+  return component;
 }
-Object.keys(EventTypes).forEach(eventType => {
-  adMobPropTypes[eventType] = PropTypes.func;
-});
-Object.keys(NativeExpressEventTypes).forEach(eventType => {
-  adMobPropTypes[eventType] = PropTypes.func;
-});
 
 class AdMobComponent extends React.Component {
   static propTypes = adMobPropTypes;
@@ -36,11 +49,7 @@ class AdMobComponent extends React.Component {
       height: 0,
     };
 
-    this.nativeView = requireNativeComponent(props.class, AdMobComponent, {
+    this.nativeView = getNativeComponent(props.class);
-      nativeOnly: {
-        onBannerEvent: true,
-      },
-    });
   }
 
   /**