Add toStructuredText to ConstantExpression and align method names with ConstantValue

pkg/compiler/lib/src/types/value_type_mask.dart

Index: pkg/compiler/lib/src/types/value_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/value_type_mask.dart b/pkg/compiler/lib/src/types/value_type_mask.dart
index ba40f24f026c2e2099b10dcf5b992e02b53417cb..1be16bacb18a4562198c09e84f0d9f209c51a80c 100644
--- a/pkg/compiler/lib/src/types/value_type_mask.dart
+++ b/pkg/compiler/lib/src/types/value_type_mask.dart
@@ -40,6 +40,6 @@ class ValueTypeMask extends ForwardingTypeMask {
   }
 
   String toString() {
-    return 'Value mask: [${value.unparse()}] type: $forwardTo';
+    return 'Value mask: [${value.toDartText()}] type: $forwardTo';
   }
 }