Implement super initializers.

frog/leg/tree/nodes.dart

Index: frog/leg/tree/nodes.dart
diff --git a/frog/leg/tree/nodes.dart b/frog/leg/tree/nodes.dart
index 890094ab5a9fad587619fa57daec3be3c7292828..17cda56cf231e343734dd54789215fc761c3f7d2 100644
--- a/frog/leg/tree/nodes.dart
+++ b/frog/leg/tree/nodes.dart
@@ -1442,3 +1442,25 @@ class CatchBlock extends Node {
 
   Token getEndToken() => block.getEndToken();
 }
+
+class Initializers {
+  static bool isSuperConstructorCall(Send node) {
+    return (node.receiver === null &&
+            node.selector.asIdentifier() !== null &&
+            node.selector.asIdentifier().isSuper()) ||
+           (node.receiver !== null &&
+            node.receiver.asIdentifier() !== null &&
+            node.receiver.asIdentifier().isSuper() &&
+            node.selector.asIdentifier() !== null);
+  }
+
+  static bool isConstructorRedirect(Send node) {
+    return (node.receiver === null &&
+            node.selector.asIdentifier() !== null &&
+            node.selector.asIdentifier().isThis()) ||
+           (node.receiver !== null &&
+            node.receiver.asIdentifier() !== null &&
+            node.receiver.asIdentifier().isThis() &&
+            node.selector.asIdentifier() !== null);
+  }
+}