Add ConstructorBodyEntity

pkg/compiler/lib/src/elements/entities.dart

Index: pkg/compiler/lib/src/elements/entities.dart
diff --git a/pkg/compiler/lib/src/elements/entities.dart b/pkg/compiler/lib/src/elements/entities.dart
index 5779cd8d5dd8f0c4491b723e2b20f9c7df967e6f..80e8489fd8ed9dba8458886644bb15fa6e82443c 100644
--- a/pkg/compiler/lib/src/elements/entities.dart
+++ b/pkg/compiler/lib/src/elements/entities.dart
@@ -206,6 +206,17 @@ abstract class ConstructorEntity extends FunctionEntity {
   bool get isFromEnvironmentConstructor;
 }
 
+/// The constructor body for a [ConstructorEntity].
+///
+/// This is used only in the backend to split encoding of a Dart constructor
+/// into two JavaScript functions; the constructor and the constructor body.
+// TODO(johnniwinther): Remove this when modelx is removed. Constructor bodies
+// should then be created directly with the J-model.
+abstract class ConstructorBodyEntity extends FunctionEntity {
+  /// The constructor for which this constructor body was created.
+  ConstructorEntity get constructor;
+}
+
 /// An entity that defines a local entity (memory slot) in generated code.
 ///
 /// Parameters, local variables and local functions (can) define local entity