Rename ClosureVariable, use separate IR forms for declaration and assignment.

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library tree_ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values;
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
 import '../dart_types.dart' show DartType, GenericType;
@@ skipping 474 matching lines @@
  * An assignments of an [Expression] to a [Variable].
  *
  * In contrast to the CPS-based IR, non-primitive expressions can be assigned
  * to variables.
  */
 class Assign extends Statement {
   Statement next;
   Variable variable;
   Expression definition;
 
-  /// If true, this declares a new copy of the closure variable.
-  /// The consequences are similar to [cps_ir.SetClosureVariable].
-  /// All uses of the variable must be nested inside the [next] statement.
+  /// If true, this assignes to a fresh variable scoped to the [next]
+  /// statement.
+  ///
+  /// Variable declarations themselves are hoisted to function level.
   bool isDeclaration;
 
   Assign(this.variable, this.definition, this.next,
          { this.isDeclaration: false }) {
     variable.writeCount++;
   }
 
   bool get hasExactlyOneUse => variable.readCount == 1;
 
   accept(StatementVisitor visitor) => visitor.visitAssign(this);
@@ skipping 411 matching lines @@
     visitStatement(node.next);
   }
 
   visitCreateBox(CreateBox node) {
   }
 
   visitCreateInstance(CreateInstance node) {
     node.arguments.forEach(visitExpression);
   }
 }