dart2js cps: Make Identical a built-in and add Interceptor to Tree IR.

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
index 443e170e67e5c651c2f7c4539f69fb1de9b08c4f..56d5896704cb1e3f6a3ebbd65b2f03489e0f879c 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -316,12 +316,6 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     return 'CreateInstance $className ($arguments) <$typeInformation>';
   }
 
-  visitIdentical(cps_ir.Identical node) {
-    String left = formatReference(node.left);
-    String right = formatReference(node.right);
-    return "Identical($left, $right)";
-  }
-
   visitInterceptor(cps_ir.Interceptor node) {
     return "Interceptor(${formatReference(node.input)})";
   }
@@ -607,10 +601,6 @@ class BlockCollector implements cps_ir.Visitor {
     unexpectedNode(node);
   }
 
-  visitIdentical(cps_ir.Identical node) {
-    unexpectedNode(node);
-  }
-
   visitInterceptor(cps_ir.Interceptor node) {
     unexpectedNode(node);
   }