Add toStructuredText to ConstantExpression and align method names with ConstantValue

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 5abb3e1dd0b086b48c4a4fa2e67d6a456db698ca..3fb28357c51d03fd311bf6467791a51f463efccb 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -1241,8 +1241,9 @@ abstract class Compiler implements LibraryLoaderListener {
         // errors instead of using a map.
         element = mainFunction;
       }
-      elementsWithCompileTimeErrors.
-          putIfAbsent(element, () => <DiagnosticMessage>[]).add(message);
+      elementsWithCompileTimeErrors
+          .putIfAbsent(element, () => <DiagnosticMessage>[])
+          .add(message);
     }
   }