make unimplemented statements throw

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index ecb00fb6fcb233249ac0d39854661b0ca9eabad3..c4cdd86025af058b033a2deba299798d83d5c987 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -1654,14 +1654,6 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
   visitBooleanLiteral(BooleanLiteral node) => js.boolean(node.value);
 
   @override
-  JS.Statement visitDeclaration(Declaration node) =>
-      js.comment('Unimplemented ${node.runtimeType}: $node');
-
-  @override
-  JS.Statement visitStatement(Statement node) =>
-      js.comment('Unimplemented ${node.runtimeType}: $node');
-
-  @override
   JS.Expression visitExpression(Expression node) =>
       _unimplementedCall('Unimplemented ${node.runtimeType}: $node');