react-native: BundleSegments: remove async/await

Reviewed By: fromcelticpark

Differential Revision: D6508646

fbshipit-source-id: 9e5c05bde5420cb030912eb187f6333af4b580f9

Libraries/Utilities/BundleSegments.js

@@ -20,15 +20,18 @@ let segmentLoaders = new Map();
  * its module. We cache load promises so as to avoid calling `fetchSegment` twice
  * for the same bundle. We assume that once a segment is fetched/loaded, it is
  * never gettting removed during this instance of the JavaScript VM.
+ *
+ * We don't use async/await syntax to avoid depending on `regeneratorRuntime`.
  */
-async function loadForModule(moduleID: number): Promise<void> {
+function loadForModule(moduleID: number): Promise<void> {
+  return Promise.resolve().then(() => {
     const {segmentId} = (require: $FlowFixMe).unpackModuleId(moduleID);
     if (segmentId === 0) {
       return;
     }
     let segmentLoader = segmentLoaders.get(segmentId);
     if (segmentLoader != null) {
-    return await segmentLoader;
+      return segmentLoader;
     }
 
     const {fetchSegment} = global;
@@ -48,7 +51,8 @@ async function loadForModule(moduleID: number): Promise<void> {
       });
     });
     segmentLoaders.set(segmentId, segmentLoader);
-  return await segmentLoader;
+    return segmentLoader;
+  });
 }
 
 module.exports = {loadForModule};