Dart2js option to dump info about compilation

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

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index 131c2761dd3397f41cf3f912d1496e84cffcdacf..8f97b54b38c1f241cf68ba2ccff1e0e165daf29c 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -333,6 +333,7 @@ class ErroneousElementX extends ElementX implements ErroneousElement {
   get patch => null;
   get origin => this;
   get defaultImplementation => unsupported();
+  get nestedClosures => unsupported();
 
   bool get isRedirectingFactory => unsupported();
 
@@ -1120,6 +1121,8 @@ class VariableElementX extends ElementX implements VariableElement {
 
   Modifiers get modifiers => variables.modifiers;
 
+  List<FunctionElement> nestedClosures = new List<FunctionElement>();
+
   VariableElementX(String name,
                    VariableListElement variables,
                    ElementKind kind,
@@ -1420,6 +1423,8 @@ class FunctionElementX extends ElementX implements FunctionElement {
   DartType type;
   final Modifiers modifiers;
 
+  List<FunctionElement> nestedClosures = new List<FunctionElement>();
+
   FunctionSignature functionSignature;
 
   /**