[dart2js] Handle injected names from late fields

Change-Id: I5ca6535a282ce8fdf4fba6cd1fa5752bce2921c9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136714
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

pkg/compiler/lib/src/js_backend/namer.dart

@@ -636,6 +636,8 @@ class Namer extends ModularNamer {
   String privateName(Name originalName) {
     String text = originalName.text;
 
+    text = text.replaceAll(_nonIdentifierRE, '_');
+
     // Public names are easy.
     if (!originalName.isPrivate) return text;
 
@@ -883,7 +885,8 @@ class Namer extends ModularNamer {
     if (_closedWorld.isUsedAsMixin(enclosingClass) ||
         _isShadowingSuperField(element) ||
         _isUserClassExtendingNative(enclosingClass)) {
-      String proposeName() => '${enclosingClass.name}_${element.name}';
+      String proposeName() => '${enclosingClass.name}_${element.name}'
+          .replaceAll(_nonIdentifierRE, '_');
       return _disambiguateInternalMember(element, proposeName);
     }