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 f06f740fc35c969fc6713a8803f4feb2f85bc097..ff2a8e0e7c11423dfadbd23e22d8a306802c2c54 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -627,6 +627,10 @@ abstract class ScopeContainerElement implements Element {
   void forEachLocalMember(f(Element element));
 }
 
+abstract class ClosureContainer implements Element {
+  List<FunctionElement> get nestedClosures;
+}
+
 abstract class CompilationUnitElement extends Element {
   Script get script;
   PartOf get partTag;
@@ -732,7 +736,7 @@ abstract class TypedefElement extends Element
   void checkCyclicReference(Compiler compiler);
 }
 
-abstract class VariableElement extends Element {
+abstract class VariableElement extends Element implements ClosureContainer {
   VariableListElement get variables;
 
   // TODO(kasperl): Try to get rid of this.
@@ -785,7 +789,7 @@ abstract class FunctionSignature {
   bool isCompatibleWith(FunctionSignature constructorSignature);
 }
 
-abstract class FunctionElement extends Element {
+abstract class FunctionElement extends Element implements ClosureContainer {
   FunctionExpression get cachedNode;
   DartType get type;
   FunctionSignature get functionSignature;