Add HCreateBox

pkg/compiler/lib/src/ssa/nodes.dart

Index: pkg/compiler/lib/src/ssa/nodes.dart
diff --git a/pkg/compiler/lib/src/ssa/nodes.dart b/pkg/compiler/lib/src/ssa/nodes.dart
index 5714e73ba9c2d92bfcfc567e8fba7aaf286e9f3d..cfee3948caee0c1f3f23a606a37a095332983cab 100644
--- a/pkg/compiler/lib/src/ssa/nodes.dart
+++ b/pkg/compiler/lib/src/ssa/nodes.dart
@@ -38,6 +38,7 @@ abstract class HVisitor<R> {
   R visitConstant(HConstant node);
   R visitContinue(HContinue node);
   R visitCreate(HCreate node);
+  R visitCreateBox(HCreateBox node);
   R visitDivide(HDivide node);
   R visitExit(HExit node);
   R visitExitTry(HExitTry node);
@@ -395,6 +396,7 @@ class HBaseVisitor extends HGraphVisitor implements HVisitor {
   visitCheck(HCheck node) => visitInstruction(node);
   visitConstant(HConstant node) => visitInstruction(node);
   visitCreate(HCreate node) => visitInstruction(node);
+  visitCreateBox(HCreateBox node) => visitInstruction(node);
   visitDivide(HDivide node) => visitBinaryArithmetic(node);
   visitExit(HExit node) => visitControlFlow(node);
   visitExitTry(HExitTry node) => visitControlFlow(node);
@@ -1649,6 +1651,17 @@ class HCreate extends HInstruction {
   String toString() => 'HCreate($element, ${instantiatedTypes})';
 }
 
+// Allocates a box to hold mutated captured variables.
+class HCreateBox extends HInstruction {
+  HCreateBox(TypeMask type) : super(<HInstruction>[], type);
+
+  bool get isAllocation => true;
+
+  accept(HVisitor visitor) => visitor.visitCreateBox(this);
+
+  String toString() => 'HCreateBox()';
+}
+
 abstract class HInvoke extends HInstruction {
   /**
     * The first argument must be the target: either an [HStatic] node, or