Add CPS IR transformation to make the JavaScript backend specific semantics explicit in the tree.

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

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index d4ba56ed2a1dd962075aa5193b503d4d0a18cce1..c983a42fb16efaeb2037ea8f917276adc5be735b 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -473,5 +473,17 @@ class Builder extends cps_ir.Visitor<Node> {
   Expression visitIsTrue(cps_ir.IsTrue node) {
     return getVariableReference(node.value);
   }
+
+  dart2js.Selector get identicalSelector {
+    return new dart2js.Selector.call('identical', null, 2);
+  }
+
+  Expression visitIdentical(cps_ir.Identical node) {
+    return new InvokeStatic(
+        compiler.identicalFunction,
+        identicalSelector,
+        <Expression>[getVariableReference(node.left),
+                     getVariableReference(node.right)]);
+  }
 }