Dart2js option to dump info about compilation

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index 52c6b30d51b9c933f4422929e223c4251f4bcc68..d1df2901056a2f0d85675eefc7d3cb9b7f262760 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -30,6 +30,8 @@ import '../scanner/scannerlib.dart' show Token,
 
 import '../ordered_typeset.dart' show OrderedTypeSet;
 
+import 'visitor.dart' show ElementVisitor;
+
 const int STATE_NOT_STARTED = 0;
 const int STATE_STARTED = 1;
 const int STATE_DONE = 2;
@@ -257,6 +259,8 @@ abstract class Element implements Spannable {
   FunctionElement get targetConstructor;
 
   void diagnose(Element context, DiagnosticListener listener);
+
+  accept(ElementVisitor visitor) => visitor.visitElement(this);
 }
 
 class Elements {