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;

[Dmitry Stefantsov, 2017/08/24 09:41:13]

Personally, I don't like modifying AST definitions because of just one
transformation.  I believe, changes here should be justified universally.
 I would prefer defining a function `bool isLoop(Statement stmt)` in
`pkg/kernel/lib/transformations/closure/converter.dart` (currently, the only
place that needs to distinguish between loop statements and non-loop
statements).

[sjindel, 2017/08/24 11:11:43]

I understand that, but I feel like determining whether a statement represents a
loop is a pretty general operation. It doesn't change the binary format anyway
-- it's just a helper function.

[Dmitry Stefantsov, 2017/08/24 11:49:57]

I agree that it's a general operation and that it doesn't change the binary
representation, but I'd prefer to have it as a part of a bigger update that
brings some kind of systematic categorization to AST nodes.  This file serves as
a reference to Kernel syntax, and auxiliary methods may bring unnecessary
questioning about the design of the syntax.

[sjindel, 2017/08/24 14:50:13]

Done.

 }
 
 /// 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: ... }`.