Fix several bugs in closure conversion.

pkg/kernel/lib/ast.dart

Index: pkg/kernel/lib/ast.dart
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index f0d508fa304f7a54799b98ecc72f1f45b07abceb..a19135607034c111754c0a87da5f30bbb714c219 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -3178,6 +3178,7 @@ class ClosureCreation extends Expression {
 abstract class Statement extends TreeNode {
   accept(StatementVisitor v);
   accept1(StatementVisitor1 v, arg);
+  bool get isLoop => false;
 }
 
 /// A statement with a compile-time error.
@@ -3363,6 +3364,8 @@ class WhileStatement extends Statement {
       body?.parent = this;
     }
   }
+
+  bool get isLoop => true;
 }
 
 class DoStatement extends Statement {
@@ -3392,6 +3395,8 @@ class DoStatement extends Statement {
       condition?.parent = this;
     }
   }
+
+  bool get isLoop => true;
 }
 
 class ForStatement extends Statement {
@@ -3429,6 +3434,8 @@ class ForStatement extends Statement {
       body?.parent = this;
     }
   }
+
+  bool get isLoop => true;
 }
 
 class ForInStatement extends Statement {
@@ -3473,6 +3480,8 @@ class ForInStatement extends Statement {
       body?.parent = this;
     }
   }
+
+  bool get isLoop => true;
 }
 
 /// Statement of form `switch (e) { case x: ... }`.