Add toStructuredText to ConstantExpression and align method names with ConstantValue

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

Index: pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart
diff --git a/pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart b/pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart
index ee4272afc8a62d8d3c892caa820a0c136fb88b23..c0bec8ae2ce6c4981c046c7e04f446f5808eec61 100644
--- a/pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart
+++ b/pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart
@@ -308,7 +308,7 @@ class LookupMapAnalysis {
       for (var info in _lookupMaps.values) {
         for (var key in info.unusedEntries.keys) {
           if (count != 0) sb.write(',');
-          sb.write(key.unparse());
+          sb.write(key.toDartText());
           count++;
         }
       }