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

pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart

Index: pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
diff --git a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
index cd92b24ede0b138d7bb829b40c154279f7237567..61a72fa0641ea908ad5e458cb068dc313423fa8a 100644
--- a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
+++ b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
@@ -512,6 +512,12 @@ class ParentVisitor extends RecursiveVisitor {
     node.body.parent = node;
   }
 
+  processLetMutable(LetMutable node) {
+    node.variable.parent = node;
+    node.value.parent = node;
+    node.body.parent = node;
+  }
+
   processInvokeStatic(InvokeStatic node) {
     node.arguments.forEach((Reference ref) => ref.parent = node);
     node.continuation.parent = node;
@@ -555,12 +561,14 @@ class ParentVisitor extends RecursiveVisitor {
     node.receiver.parent = node;
   }
 
-  processSetClosureVariable(SetClosureVariable node) {
+  processSetMutableVariable(SetMutableVariable node) {
+    node.variable.parent = node;
     node.body.parent = node;
     node.value.parent = node;
   }
 
   processDeclareFunction(DeclareFunction node) {
+    node.variable.parent = node;
     node.definition.parent = node;
     node.body.parent = node;
   }
@@ -618,6 +626,10 @@ class ParentVisitor extends RecursiveVisitor {
     node.object.parent = node;
   }
 
+  processGetMutableVariable(GetMutableVariable node) {
+    node.variable.parent = node;
+  }
+
   processCreateInstance(CreateInstance node) {
     node.arguments.forEach((Reference ref) => ref.parent = node);
   }