[dart2wasm] Add export name minification to _WasmImporter.

Change-Id: Iaddd056a10b0a9d315ffac120a36d9722dbacccc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/446991
Reviewed-by: Jackson Gardner <[email protected]>
Commit-Queue: Mayank Patke <[email protected]>

Author: fishythefish

pkg/dart2wasm/lib/exports.dart

@@ -56,6 +56,8 @@ class ExportNamer {
 /// The `exportDynamic___` methods add relevant associations to the above
 /// mappings and add the given exportable to the Wasm exports of the specified
 /// module under the computed export name.
+///
+/// For deferred imports, the [export] method is sufficient.
 class Exporter {
   final ExportNamer _namer;
   final MainModuleMetadata _mainModuleMetadata;

pkg/dart2wasm/lib/translator.dart

@@ -2660,7 +2660,8 @@ abstract class _WasmImporter<T extends w.Exportable> {
     if (key.enclosingModule == module) return key;
 
     final innerMap = _map.putIfAbsent(key, () {
-      key.enclosingModule.exports.export('$_exportPrefix${_map.length}', key);
+      _translator.exporter
+          .export(key.enclosingModule, '$_exportPrefix${_map.length}', key);
       return {};
     });
     return innerMap.putIfAbsent(module, () {