Rename ShareSheet

Summary:
From the name it's not clear that this is actually a fork off the "Share File"
variant of this. I'm planning to bring the two together as they share most of
the code, but for now this makes it a bit clearer.

Reviewed By: jknoxville

Differential Revision: D17786570

fbshipit-source-id: 8def3301ee4f79741391dc7e0b6a33a5fd7aa2c3

src/chrome/ShareSheetExportUrl.tsx

@@ -87,7 +87,7 @@ type State = {
   statusUpdate: string | null | undefined;
 };
 
-export default class ShareSheet extends Component<Props, State> {
+export default class ShareSheetExportUrl extends Component<Props, State> {
   static contextTypes = {
     store: PropTypes.object.isRequired,
   };