dart2js: fix for https://github.com/dart-lang/sdk/issues/24412

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

Index: pkg/compiler/lib/src/js_backend/codegen/codegen.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
index 963f1d7f43ae700436985490c217268f38209910..791677068760e9f52c606fbbc7d3729894f60943 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
@@ -639,6 +639,14 @@ class CodeGenerator extends tree_ir.StatementVisitor
 
   @override
   void visitTry(tree_ir.Try node) {
+    void register(ClassElement classElement) {
+      if (classElement == null) return;
+      registry.registerInstantiatedClass(classElement);
+    }
+    // We might catch JavaScript exceptions.
+    register(glue.jsPlainJavaScriptObjectClass);
+    register(glue.jsUnknownJavaScriptObjectClass);
+
     js.Block tryBlock = buildBodyBlock(node.tryBody);
     tree_ir.Variable exceptionVariable = node.catchParameters.first;
     js.VariableDeclaration exceptionParameter =