Scrub all non-identifier characters from JavaScript class names

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

Index: pkg/compiler/lib/src/js_backend/namer.dart
diff --git a/pkg/compiler/lib/src/js_backend/namer.dart b/pkg/compiler/lib/src/js_backend/namer.dart
index 52eaa5591b44c3be529537b2df96bd9e34670b12..a5b21318606b222973b2e078900ebfb7e93ac1b9 100644
--- a/pkg/compiler/lib/src/js_backend/namer.dart
+++ b/pkg/compiler/lib/src/js_backend/namer.dart
@@ -1286,9 +1286,11 @@ class Namer {
   /// Returns a proposed name for the given typedef or class [element].
   /// The returned id is guaranteed to be a valid JavaScript identifier.
   String _proposeNameForType(Entity element) {
-    return element.name.replaceAll('+', '_');
+    return element.name.replaceAll(_nonIdentifierRE, '_');
   }
 
+  static RegExp _nonIdentifierRE = new RegExp(r'[^A-Za-z0-9_$]');
+
   /// Returns a proposed name for the given top-level or static member
   /// [element]. The returned id is guaranteed to be a valid JavaScript
   /// identifier.