Remove more type casts

pkg/analyzer/lib/src/dart/ast/utilities.dart

Index: pkg/analyzer/lib/src/dart/ast/utilities.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/utilities.dart b/pkg/analyzer/lib/src/dart/ast/utilities.dart
index ee59dd66bca58e2a31e122da00f235e1f5638b9c..a87c085386de557a0b5d861bd7726f0006ea8e2c 100644
--- a/pkg/analyzer/lib/src/dart/ast/utilities.dart
+++ b/pkg/analyzer/lib/src/dart/ast/utilities.dart
@@ -2316,10 +2316,11 @@ class ConstantEvaluator extends GeneralizingAstVisitor<Object> {
     for (MapLiteralEntry entry in node.entries) {
       Object key = entry.key.accept(this);
       Object value = entry.value.accept(this);
-      if (key is! String || identical(value, NOT_A_CONSTANT)) {
+      if (key is String && !identical(value, NOT_A_CONSTANT)) {
+        map[(key as String)] = value;
+      } else {
         return NOT_A_CONSTANT;
       }
-      map[(key as String)] = value;
     }
     return map;
   }