Improve tracking of the type of fields after object construction

lib/compiler/implementation/elements/elements.dart

Index: lib/compiler/implementation/elements/elements.dart
diff --git a/lib/compiler/implementation/elements/elements.dart b/lib/compiler/implementation/elements/elements.dart
index 12ffc0f8d3115878728d63cd1e9dc9b764b68d1e..1878a37c3221e27c4bf750c76444dd147556fd00 100644
--- a/lib/compiler/implementation/elements/elements.dart
+++ b/lib/compiler/implementation/elements/elements.dart
@@ -118,6 +118,8 @@ class Element implements Hashable {
   bool isInstanceMember() => false;
   bool isFactoryConstructor() => modifiers !== null && modifiers.isFactory();
   bool isGenerativeConstructor() => kind === ElementKind.GENERATIVE_CONSTRUCTOR;
+  bool isGenerativeConstructorBody() =>
+      kind === ElementKind.GENERATIVE_CONSTRUCTOR_BODY;
   bool isCompilationUnit() {
     return kind === ElementKind.COMPILATION_UNIT ||
            kind === ElementKind.LIBRARY;